After infiltrating the Paranormal Liberation Army, Keigo found himself paired up with one of Shigaraki's closest allies, you.
Despite being that little bit mixed up in the head, you were a generally nice person who did really seem to try and make him feel comfortable there despite not knowing his true intentions. Hell, you were one of his biggest intels when it came to telling the HPSC information because you'd trusted him.
Unfortunately you were a big liability. Being one of Shigaraki's most trusted allies and generals, you were powerful and would do anything to protect a freind, you'd made that very clear in your graphic detailing.
That was the one thing Keigo was most worried about when all of the heroes began to plan a surprise attack on the Paranormal Liberation Army.
He was told point blank that you needed to be taken out of the picture as soon as the attack started, you were too much of a risk if you'd used your quirk, especially after you'd somewhat gotten over your mental traumas, letting you use your quirk to it's best.
Mabye that's why Keigo couldn't bring himself to actually kill you. Mabye that's why he tried to find another way to keep you away from the fight, even if it did mean betraying your trust.
Having cornered you in a room and keeping you pinned down with his feathers, Keigo stood by the doorway, watching you carefully as the two of you talked back and forth.
"I don't want to do anything, you just need to stay still and everything will be fine-!" Keigo tried to reason as he felt you try and move from your spot, repositioning his feathers to strike if need be, "You're a good person, yknow? I know you are, I know where you can get help, you can be something better-" He went on.