Actually getting settled back into their respective homes was almost comically quick and easy: Since Pinkie Pie was the premiere party planning pony of Ponyville, there wasn't anypony at the town border waiting or expecting them. In fact even if there had been, they still might have been caught by surprise since he and Pinkie got back after just six days, ahead of their projected plans.
They'd had the Crystalline Caponata for dinner the previous night and then traveled through the dark rather than waste the buff on sleeping. Not that they needed sleep, full of energy as they were! Now they were back in town and getting back into the swing of things felt very natural. They split up outside of Sugarcube Corner with one goodbye kiss (and then a few extra for good luck) and while she went inside, he made his way back to the Library.
Spike raised his voice to the top and bellowed through the door.
"Hey Twilight, I'm home!"
There was no reply.
He looked around the first floor for a bit and saw the lab marker by the basement door was flipped: That meant somepony was down there working. Since it was only the two of them there wasn't a more complex system in place, no signal for "in the lab, do not disturb" or "in the lab, soundproofing magic active" or whatever. In the past Spike was pretty good about trying not to disturb her during times like these, barring major emergencies. Now he was more confident in himself and decided to head down immediately.
There were wards in place, but not particularly strong or unusual ones: Nothing for filtering the air or preventing concussive blasts. The main component Spike recognized was the soundproofing, which made some sense if she was taking notes out loud on her own again. The stairs were thankfully all clear of blockage, be that magic, debris, or forgotten books: For all that Twilight showed a fastidious nature day to day? She could still get sloppy when she was in the research groove.
When he hit the bottom he was surprised to see two things: First, the combat wards were also up, protecting the area from collateral damage. Second, Twilight wasn't alone in the lab: She was here with another unicorn, trading blows and spells across the expanse. He specified blows in addition to spells because the guest wasn't fighting with their magic at all.
Rather than step inside and breach the wards, Spike decided to do the first thing that came to mind in this sort of situation: He activated the spirit of battle from his Combat Discipline, dropping down into his own admittedly generic battle-ready stance.
Both fighters clearly recognized the sense of his presence, and they waited until they were done with their current exchange (a backhoof uppercut smashing apart a wave of bright sparks) before turning to face him. Twilight's eyes lit up and she quickly bounded over to undo the protections and let him inside, while their guest...
Lyra (Heartstrings at the moment) raised a bruised hoof and waved vigorously.
"Welcome back!"
He assumed that's what she said anyways: Soundproofing wards and all that. He was no lip reader, although he really should invest in that... Oh wait, would his subtitles work under these conditions? Previous testing had shown some degree of audibility was needed, but this was kind of a corner case... Eh, they could test it later.
He waited until the wards dropped (visible to him thanks to both the Dragon's Mind and Twilight's conveniently-placed signaling sigils) before waving and replying back.
"Hey Twilight, hey sensei!"
Lyra nearly smacked her own face with the same hoof she used to wave before.
"What did I tell you about being formal?"
"That it annoys you to no end and makes you feel old, so every time I do it I have to run a lap or two around Ponyville?"
He just sat there waiting until she groaned, realizing the problem.
"...I probably should have set the punishment to something you wouldn't just enjoy the benefits of."
Spike just grinned at that, a little preoccupied with a sudden armful of Twilight to reply any more.
She pulled back from the welcoming embrace and gripped him by the shoulders.
"Well you made it back in fantastic time!"
"Pinkie and I didn't feel like taking too many scenic routes. Maybe another time?"
Twilight sighed and pulled him across the wards so she could bring them back up.
"Don't tell me either of you are planning to walk back from Canterlot again."
He shrugged.
"Maybe not back, and maybe not both of us. But you and me are heading up again to meet Shining and Cadance once they're home, right? Taking the route there on foot is not off the table."
A longer, more exasperated sigh was the only reply he got from Twilight. Lyra clopped her hooves together to get his attention in the meantime.
"Is that where you've been this whole time?"
"Yup! Kind of a last-minute idea, but it worked out pretty well. I learned a lot in a little time, even if it didn't correspond to very many skills... haha, although that kinda changed on the way back too!"
The wards sprang to life behind him, and he immediately noticed that not only were the combat and soundproofing both active, so were a half-dozen of the others and one or two he'd never seen before.
"I guess I'm not the only one who was busy?"
Twilight shot him a wide and mischievous smile.
"Of course not! I have to keep testing myself, especially after... well, you know. Progress!"
He nodded sagely: Probably not the time to tell Lyra about the whole 'Princess relationship' thing.
"Progress."
Lyra slowly rolled her neck from side to side, cracking her joints in a classic display of intimidation.
"So are we making this a free-for-all? Because I do not envy a one-mare team battle against an Element of Harmony and a dragon, much less a dragon with your freaky powers."
Spike put up a claw, even as he started mentally preparing himself. Physical stretches had long since lost much purpose before a fight: Still useful for training but not critical for avoiding a sprain.
"Hey, speaking of which, before we get started? Why were you two even fighting to begin with?"
"Oh! That's actually a very funny coincidence. Lyra came to the Library a few times while you and Pinkie Pie were still on the road, since nopony back home knew about your... last-minute plans. I struck up a conversation with her about your recent training, and one thing sort of led to another!"
Lyra stuck out a tongue at that description and made her own summary of the events.
"To make that long story short, you left me without a sparring partner so I took it out on her."
"Ohho, does that mean I'm already doing better than everypony at the dojo?"
"Hay no, it just means you're a much weirder guy to fight. They're all definitely stronger, but in a way I'm totally used to. There's not a lot to learn from us fighting each other anymore unless we go for blood. But a pony like Twilight, or something like you? That's unique, and pretty cool to try out."
Twilight had finished her own preparations and stretches and had already lit up her horn... As well as several strange new devices he had never seen before. Either her time alone with the Princess back in Canterlot had provided a ton of information, or she'd been brewing new ideas constantly in the back of her mind... Probably six of one and half a dozen of the other.
On the other end of their impromptu triangle, Lyra leisurely fell back into her two-hooved walking style, bringing both of her forehooves up as if she were mocking Spike's own stance. That's what an outside observer would assume, but Spike had been on the receiving end of all four of those hooves hundreds of times: There was no mockery here. She was just a scarily adaptable pony with her own sense of what worked and what didn't.
That left him standing in his 'corner' of the metaphorical squared circle, Gamer nature shining in his lack of preparation. Nothing could tie him down or bind his limbs in a way that mattered, no attack could disable him, and as for a form... He knew there was power there, waiting for him. It just wasn't the time for him to take it. If he jumped in half-baked to try and get himself stronger faster? It would burn him in the long run.
That cinched it: He decided that for this fight at the very least? He wouldn't even touch his Discipline or any of its attacks. Just a nice clean battle between the three of them... As nice as any battle could get anyways, and as clean as anything involving these two unicorns could be.
None of them wanted to throw the first blow, so they all spent a moment just feeling out the tense air and waiting to see a gap... Twilight must have seen something, because her magic cracked out in a shimmering wave to send one of those compact objects across the room at him, and another to Lyra at the same time. Lyra braced herself to avoid it and neutralize whatever came out, but Spike used his most consistently-powerful skill in response instead.
"Observe."
Just Some Random Objects
An arbitrary assemblage of mechanical parts designed by Twilight Sparkle to give off the impression of being dangerous enchanted weaponry. There's even a supply crystal inside providing magical energy to a meaningless circuit so that it has the aura of an active magitech device.
He wanted to laugh and clap at that, but he instead decided to just bat it out of the air and rush at his friend-mentor-mother-keeper. Lyra was too busy playing keep-away with Twilight's projectiles to see that she was charging a much more dangerous spell behind her feints, although knowing Lyra that might have been her own feint in response... Which is why Spike decided to attack Twilight first under the circumstances.
[Danger below!]
That nearly got him a dense slug of raw thaumaturgical might to the chin for his trouble. The floor itself shot a blast of pure magic straight up at him, and he gawked for a second. Twilight had rigged the wards to give herself an advantage? He could have sworn that was against their usual rules...
He figured out the loophole before she even finished making her self-satisfied grin.
"I would have had all the same protections if I'd just stayed put on my starting spot, huh?"
"Taking into account home field advantages are very important for replicability!"
They shared this exchange over the course of a few quick strikes: Twilight using her telekinetic control of the fake devices to use one as a combination cudgel and shield in contrast to his own claw strikes and brief gouts of fire breath. He had enough faith in Twilight's combat wards that he could use somewhat-dangerous attacks like that in a friendly setting...
[Bloodthirst detected!]
[Danger from behind you!]
Well, a formerly friendly setting.
"I don't think Lyra liked your little joke."
This time Twilight's grin was downright smug.
"Who said they were all jokes?"
The device she'd been using to parry suddenly popped open and unleashed a camera flash strong enough to overwhelm even his nictating membranes... Although the blindness literally only lasted as long as the flash itself thanks to the Gamer's Body. That was still enough time for Lyra to barrel hooves-first into their duel and turn it into a much messier brawl.
He'd gotten her to take him seriously during a few of their duels back at the dojo, and this felt like one of those times. Rather than just using hoofwork and strikes to fight, her hooves were coated in a thick aura of glittering golden magic. Spike knew to be wary of taking a hit: Something about the spell she was using made her strikes hit like they came from a pony Macintosh's size despite Lyra keeping all of her normal speed and agility.
So now they were stuck in an interesting triangle strategy: Lyra had the most combat experience but the least familiarity with the terrain and the wards. Twilight had an unknown amount of her new experiments and tricks but the least actual combat experience. And that left Spike himself, maybe the most dangerous but the youngest and the one with the most reasons to hold back. They both knew he could regenerate and ignore any injury, but he had to be careful to not overstep what the wards would safely buffer for them.
Eventually the tension broke when he stomped, hard, Alter-ing the flow of the ward's magic to cause a disturbance in the air. His half-baked Discipline wasn't enough to mess with their operation, but it still caused both unicorns to startle and leap into action themselves. Twilight switched to traditional unicorn magic for her attacks, while Lyra started making sweeping leaps and moves that covered the ground between both opponents.
Exchanges and trades broke out like that repeatedly for around half an hour. After that point they all stepped back and just... stopped. This was never going to end effectively: Spike had Gamer's Body resilience, Lyra had unknown years of experience and stamina training, and Twilight Sparkle was literally Twilight Sparkle, Element of Magic herself. Even overlooking their respective weaknesses (IE Lyra's unfamiliarity, Twilight's lacking battle tendency, Spike's need for restraint) still created enough tradeoffs to make this mad scramble into a perpetual stalemate.
Twilight was the one to suggest they actually call it.
"Pax?"
Spike nodded.
"Pax."
Lyra seemed far less satisfied, but eventually (grudgingly) fell down on her flanks with a huff.
"Fine."
In what felt like a conciliatory gesture, Spike prepared a bracing lunch for all of them afterwards. He was still short on new core recipes for the Dragon's Kitchen, but the window of time was still good to show off the Crystalline Caponata. Given how much effort they had just put into their battle, the dish went over extremely well: Eggplant, squash, onion, celery, tomato... all sorts of the best local vegetation got melded together in the briny-spicy embrace of capers and pickled peppers, with just a hint of dense green olives they'd picked up at a roadside market a day or so outside of town.
Lyra and Twilight both praised the flavor, but once the buff effects kicked in they were even more impressed: Lyra immediately started testing out her improved potential while Twilight roasted him for details almost as much as he had roasted the veggies! He got out from under the storm of her impending research binge by showing her the limitations, which only put a bit of a damper on it.
Eventually Twilight smiled and dropped that subject, looking at him happily.
"...Proud of you, Spike."
"You too, Twilight: I didn't think I'd come home to find you'd turned into some kind of schemer!"
She blushed and waved a hoof at him, even as Lyra did kata in the background.
"Oh hush. I just wanted something to even up my chances with a proper fighter like Lyra... My own magical combat skills are nowhere near some ponies, even with all the time you and I spend trying out new techniques."
Lyra's voice came out steady despite the heavy exertion she was putting herself through, performing some kind of upside-down full-body inversion kick that shook the air around her afterwards.
"Offer still stands!"
Spike looked between the two of them before settling on Twilight.
"Offer?"
"Eeeh, Lyra wanted me to consider joining you two at the dojo, or even coming on my own time... I'm not really opposed, I just don't know if it's for me."
He thought back to Ardor Ray and Lilac Lack, and to the Princesses...
"I think it might be a good idea! You were wondering about how your level stacked up to Shining Armor back then, right? I bet you it'd stand up a lot better if you really started to learn your own style of combat."
She was silent for a while before shaking her head.
"I don't think you're wrong Spike, but I also don't think that the way Lyra does things is for me-"
"Exactly! I said your own, yeah? I mean your own. Just because you'll be learning a foundation from her and the other ponies at the dojo doesn't mean you'll be copying them word for word. It's like, uh, a thesis project! You get the basics down from instructors and then find your own path to the top."
That definitely seemed to bring her back around on the idea, although she was still quiet for minutes at a time once they all resumed eating, and neither he nor Lyra got a response either way yet.
Eventually the time came where Lyra planned to head out, but Spike held up a claw one more time.
"Actually, before you go... I kinda had a breakthrough in Canterlot. And another on the way home."
Lyra elbowed him with a big smile.
"Oh yeah? Made some big discovery out in the woods, maybe found a secret path to power like the colts in those Neighponese novels always do?"
Spike hadn't read too many of those books, but he'd seen plenty of back cover patter and played a game or two from similar settings. He decided to reply with an appropriate unsubtle metaphor.
"No, more like... progress in my mental realm."
That sobered her up immediately.
"Oh yeah?"
He nodded and gestured over to the laboratory stairs, from their spot at the dining table.
"Want to go back downstairs for one more demonstration? I wanted to try something."