Cellbit kidnapped by Cucurucho, being trained and tempted with blood and violence until he's just reacting on animal instict and has accepted to be his beast.
They had been looking for him, having lost track of him after the hunger games and having being fascinated to hear about he progressed and changed, so when they find him on the fuga island cave they jump on the opportunity. They experiment on him and get potions into him to make him more animal like too, wanting to see how his body will respond after having done all the other hybrid experiments.
Cucurucho loooves to see this guy who was so dangerous and survived every horror and somehow escaped them as a dumb teenager defeated by him, it motivates him and all his workers to see how capable the Federation can be. He loves to use him to destress, having him at home to go fuck whenever the people on the island are getting on his nerves. He uses him as a treat for his workers too, rewarding their hardwork in their very important enterprise.
And then there's Bagi, the only person who managed to get out of their island because they got distracted and expected the hold they had on her parents to work enough. Bagi who they send to the island and have her remember to see her crumble, see her defeated after all the trouble she's given them on the outside world, all the things she's uncovered that it's been hard for them to keep hidden.
But instead of crumbling she just becomes even more of a pain, going in a revenge spree against them and getting organized with other people on the island.
So they say, okay? You want your brother back? And they bait her, they make her choose whether she wants to go alone to what is obviously a trap, but with proof that Cellbit will be there, or stay back and be smart and talk to other people and risk Cellbit disappearing again. Telling her that if she tells anybody they will murder him.
The federation didn't understand familial love before, it's why they didn't expect Bagi to get out of the island and dedicate her life to finding Cellbit, but they understand now that it's very strong, it's how they got the idea for the eggs in the first place.
Of course Bagi goes and fights to try and escape with Cellbit, and even when she sees there's no way out she still doesn't lose her determination.
She's heartbroken when she sees that Cellbit doesn't remember her, but she doesn't give up, trying to talk to him to make him remember.
And then Cucurucho says something to Cellbit and he finally looks at her and jumps on her and starts biting her and touching her, his gaze with nothing behind it except want and curiosity.
Cellbit doing to her what they've done to him, looking up at Cucu at first for approval... But very soon remembering what he likes and wants and just going for it... Having these flashbacks and replicating them... Eating off chunks of Bagi and making her eat some...
It makes Cellbit happy and means they have to worry less about him biting and trying to attack them.
They have pictures that they pass around of them at meetings.
I think they'd want to use Bagi as well (specially Elena) but Cellbit would not want to share and get very agressive so rather than it being a whole thing where they humiliate him by doing it in front of him, they prefer going behind his back and fucking her whenever they take her to be healed or killed off and respawned. Cellbit doesn't think anything of it because she just smells like a hospital by the time she gets back, though of course he makes sure to mark her and make her smell like him again.
(Also I think having Bagi around makes Cellbit remember some images and such from his past although he can't place them, which leads to him hugging her or brushing her hair because he remembers somebody doing that to him and it feeling nice and it makes it even worse for Bagi to have those few moments of softness and remember their past together)