It was as they were taking a deliciously sexy shower - Celestia groaning deeply as Daniel furiously took her equine-style - that her human leaned over her back and nipped her ear. "Change your size," growled he as he thrust himself within her, driving her mad, "so that you're as small as a normal pony mare..." As the teeth of her - 'apexpredatorownerohfuck...!' - beloved closed upon the tip of said ear, not hard enough to draw blood though enough to draw a little scream from her, Celestia whimpered, gasped, coughed! "W-Wait..." stuttered she and he did; a whimper escaped her as Daniel pulled away, giving her the time needed to come down from the euphoria he'd been putting her through and focus her magic.
Then... with a simple shrinking spell, what he asked was done - the alicorn mare was now of a smaller size, similar to that of her Little Ponies. No sooner had she cast the spell then a shriek escaped her as her beloved human picked her up in his arms; then she was keening in bliss as she was pushed against the shower wall by Daniel as he began to rut her furiously, ravishing her, pounding himself deep into her depths again and again. Supported only by his hands - 'ohfausthishands...!' - about her flanks, and the ceramic-tiled wall at her back, it was all she could do to just hang on to her sanity, pounding her hooves futilely against his chest as she snorted lost in her lust, eyes rolling wildly. Up, up, up rose she, rocketing towards perhaps the most powerful climax she'd ever had. "Nuhh-Danhhh-Ohgoaah...!" babbled she; then she was silenced with a kiss, a searing, fiery kiss, which she returned as desperately she locked her forehooves about his neck.
Pulling from her - only to crash deeper into her than before - Daniel sheathed himself inside her once more, twice more... and then Celestia's eyes snapped open as she howled with her release, her essence gushing from her heated depths into the water as she bucked and humped against him like... like a whorse; an uncontrolled surge of magic loosing from her horn to enwrap them within a cocoon of light! Seconds later, Daniel groaned deeply as he felt her muscles clenching and rippling about his length, spilling his seed within her, again and again, causing a metaphorical explosion within her each time. As their passion rose and fell, rose and fell, rose and fell, Celestia would let out a high-pitched neighing-scream... until at last, mentally blown apart by the indescribable feelings of... whatever that was she'd experienced... Celestia crashed back to Earth, an utterly shattered, insensate pile of mush barely resembling a mare, let alone a Princess!
After that... well, she could barely remember what happened. She might've heard the water being shut off; she thought she remembered being toweled down... It was her Daniel that toweled her off before he led her to the bed, wasn't it...? A duvet clad her burnt out body, and her hooves and wings were wrapped about another being; someone was with her... - 'Warm-no-fur-notponyhuman...' Nosing foal-like into human hair she smelt -'familiar-friend-love...' Gradually, as her senses returned, swallowing thickly - struggling to moisten a throat raw from screaming - Celestia rasped, "Duh-Danh...Daniel?"
Affection and love welled within her - her eyes misting with blissful tears - as Daniel, her beloved Daniel, pulled her close to him, snuggling with her as he softly kissed her forehead, above her horn. "Yes, Celestia, it's me. Hush now, love... hush now. There's a good girl..." Cocooned within the bed, wrapped up warmth and musty comfort, the alicorn mare swiftly shut her eyes. Soon, Daniel joined her and together, human and alicorn mare slept deeply. When they awoke the next morning - Celestia having returned to her normal size as the spell gradually lessened then wore off during the night - as Daniel stroked her cheeks and gently combed his hands through her mane, he softly stated. "Good Morning, love. How do you feel?"
The princess pony didn't answer her beloved at first; instead she stretched languidly, before she winced and uttered, "Mmh... sore..." At this, Daniel couldn't help it - he grinned a chuckle escaping him - then upon seeing his beloved's miffed expression he kissed her on the nose as he whispered, "Sorry..." Snuggling closer to him such that her barrel was against his body Celestia nosed and nuzzled him affectionately here and there. "Daniel, oh my Daniel... goddess, don't be!" nickered she. "I might be sore for a while, but after last night... mhh... I. Regret. Nothing. It was totally worth it..."