Notes

chapter three: it's been maybe two or three weeks since Karai was mutated. in that time the turtles' birthday passes (they're 16!) and they've been patrolling. one evening raph sees Leo go out on patrol alone, as he's been doing a lot lately, and this evening raph decides to go with him. while they're out, they run into karai being attacked by the foot, and they jump in to help her. she recognizes Leo and agrees to come back, and Raph's like how the fuck are they going to get her back, except then she changes back to a human. they bring her back tot he lair

chapter four: Karai's not entirely there? but she seems to recognize them all and she doesn't protest donnie taking blood samples. he puts the turtle mech on hold to work not he cure for karai. in the weeks while he's working, they (mostly splinter and Leo) focus on bringing Karai's mind back. mikey and raph help a lot in this regard because Mikey's mikey and raph likes to spar with her. donnie only really emerges from the lab to eat, sleep occasionally, practice, and sometimes go on patrol with his brothers. it takes him about two weeks to come up with a retromutagen.

chapter five: the retromutagen works partially? it gives her greater control over her shapeshifting and it returns her mind to her. theres a lot of thanking and apologizing, but eventually everyone forgives her. so she moves permanently into a room at the lair. donnie takes samples of her venom (to make an antivenin, he claims, but everyone knows he's gonna try to weaponize it lol). she goes out on patrol with them, but they notice the foot are still out in force looking for her so they resolve to lay low and focus on the Kraang. donnie gets back to working on the turtle mech

chapter six: donnie takes more blood from karai and himself. they have training. donnie takes more blood. mikey asks why donnie only takes blood from himself, especially because he's taken so much recently that his inner arm is bruised all to hell. donnie tries to play it off but they can tell and they won't let it go, so he's like oh my god fine and calls a family meeting. he explains the whole thing about their genetics and everyones like aww okay we're sorry you're upset but literally no one cares lol. donnie goes back to building the turtle mech and they go on a family trip to the scrapyard, just the brothers. they talk a bit about karai and the foot and shredder, and about the Kraang and the incoming invasion.