Sadness
Twilight woke up feeling sad, woeful, despondent, and redundant, tears streaming from her large anime eyes, down her adorable face, and onto her fluffy horse chest. She got up off of her bed, and walked into her bathroom, sobbing with every step. She brushed her teeth, using her tears to wetten the toothpaste, and then took a short shower, during which she cried and thought about how pointless life is.
Having done enough hygiene things, she slowly shambled down the stairs, trying not to slip on her tears. Once she reached the living room, she heard a knock at the door. Her instincts kicked in, and she went to answer the door, contemplating suicide the whole time she was opening it.
Twilight was greeted with a crying, panicked-looking Rarity, and a shaking Sweetie Belle who was also crying and had a black eye.
"Twilight," cried Rarity, "please you must take care of Sweetie Belle, our parents beat her half to death and kicked her out of the house for being gay, but not before dad tried to rape the gay out of her, and also I can't take care of her because I was diagnosed with stage four breast cancer."
In response to this news, Twilight cried, which means "yes" in Equestria because everyone is so sad. Now burdened with an abused child, Twilight made her way outside, as she had to run some errands.
The first thing she saw when she opened her door was a puppy get kicked in the ribcage and thrown into the street, where it was promptly trampled to death by traffic. The puppy's caregiver, Scootaloo, who was a homeless orphan who'd had to resort to child prostitution, ran to the puppy's crippled body and cried as she tried to comfort it in its final moments. She too was then stampeded to death.
Twilight sobbed at the sight and walked down to the market, where she was met with two starving children begging her for money. She reluctantly declined now that she had a kid to feed, and walked past them. The two orphans cried and clutched their bellies, trying to stave off their hunger pangs.
As she bought her things, Twilight saw many sad sights, like a baby bird with a broken wing being abandoned by its mother, and subsequently eaten by an alley cat. Once she was done with her shopping, she headed over to Sugarcube Corner to play with Pinkie Pie. She entered the bakery, and headed up to Pinkie's room.
What Twilight saw when she entered was Pinkie dangling from a noose, completely lifeless, with a note clinging to her chest. Twilight read the note.
Dear friends and family,
I can no longer go on living like this. Every day I feel like killing myself, and it's all Twilight's fault. She's a terrible friend, and with my last words I curse her
Twilight cried and cut herself, until she heard a gasp from behind. She turned to see Mr.Cake standing in the doorway with tears in his eyes. He read the note, and literally kicked Twilight and Sweetie Belle out of his house, before murdering his wife and kids in a fit of rage.
Then, just outside of Sugarcube Corner, Twilight saw a truck full of blind puppies crash into a school for the deaf, the shrapnel from which killed Applejack right in front of AppleBloom who cried a whole lot. Her tears caused a handicapped child who was just learning to walk again to slip and break his spine, which crippled him forever.
Then some Japanese lady showed up and started crushing kitten heads with her high heels, and people just stood and watched. Fluttershy saw this happen while she was out giving physical therapy to an orphaned family of crippled ducklings, and killed herself, ensuring that her hundreds of animals would slowly starve to death.
A cop who had a pregnant wife and was two days from retirement showed up, and was gunned down by the Japanese lady.
The Japanese lady then lit a special ed building on fire, and when Rainbow Dash rushed in to save everyone, her wings got burnt off. Knowing that she would never fly again, Rainbow stayed in the fire, burning herself to death.
Twilight decided she'd had enough social interaction for one day, so she started to head home. On her way she passed by starving Africans being beaten in the street, and the only guy who tried to save them being dismembered and castrated.
When she got home, Twilight spent some time drinking and looking at old pictures that her lost daughter had drawn. They were all about how she wished she didn't have to die, and how she was so sure the doctors could save her. Unfortunately they couldn't, and after a long battle with childhood obesity, she'd died. Twilight ruminated on this fact, as well as the fact that every attempt at another offspring had ended in miscarriage and divorce.
Now that she was a princess of course, she had two options for the rest of her life. Either live and watch everyone she'd ever love slowly waste away and die, or die empty and alone.
She was roused from her thoughts by Sweetie Belle timidly asking for some lunch, and then recoiling as if she expected to be beaten for even asking. Twilight sighed, got up, and made some lunch for her and Sweetie Belle, then sat on her sofa. She munched away at her lunch in silence, her endless tears adding a salty flavor to her lunch. The lunch that reminded her of the time the entire town had gathered together to publicly hang Derpy for a crime she didn't commit, right in front of her daughter Dinky who'd had leprosy at the time. Thankfully Dinky no longer had leprosy, because she'd starved to death shortly after her mother was murdered.
Not wanting to dwell on the past, Twilight Sparkle decided to fall back on the only thing in life that gave her any modicum of happiness: books. So she opened up a magazine, saw that Caitlyn Jenner had won woman of the year, and killed herself.