selfship lore lets gooo
first meeting
The lab Kerberos works at is on Team Galactic's payroll. Usually, one of nyctos coworkers is in charge of contacting the team whenever needed, but they're absent for one time-sensitive meeting, and Kerberos takes up the role. While Charon is on the other end of this meeting, and the two end up genuinely connecting.
The two dance around the issue for a while, though. They only really start calling each other friends once Charon catches Kerberos battling a grunt who was insulting him behind his back. They weren't the type to actively challenge people, and they usually weren't the type to battle on the clock. They'd been targeting anyone who was too cowardly to insult Charon to his face. They knew Charon could take any negative attention, but going behind his back about it annoyed Kerberos enough to start battling.
They become very close friends, even if they can't express it well. Their closeness is more obvious when they're together, a sight which few people are invited to. The other commanders have seen them together, and Cyrus is... aware of Kerberos' existence.
pining
kerberos' side
Kerberos falls in love with Charon very, very slowly. It takes months, but once they realize they're in love with him, they physically can't be normal about it. They know him. They know he'd sell anyone around him to Heatran for a single corn chip. They'd have better chances with everyone else in Sinnoh. They'd have a better chance of fishing up six Feebas, refusing to evolve any of them, and becoming Champion with them. They resign themself to keeping their feelings a secret, and making the most out of any affection they can wring out of him.
charon's side
Charon doesn't really... think too hard about his feelings for Kerberos. He doesn't fall in love often, and he knows he's not conventionally attractive, especially at his age. Of course he's close to Keberos, and of course he think's they're attractive, but only aesthetically, in a perfectly reasonable, logical way. No romantic feelings here!
However, a year or so into their friendship, Kerberos calls in sick when they're scheduled for another meeting with Charon. It isn't until he's already dropped everything, come over to their place, and actively caring or them that he realizes just how unlike him any of that is. Kerberos is already coping with their crush, and sick enough to not question how much Charon went out of his way for them.
When he gets home, he's still stuck on it. After days on ruminating on it, he realizes he's in love with Kerberos. Which only makes being in their presence make him feel like a dumb teenager. It's incredibly embarrassing, but he knows he can't deny himself something he wants. Besides, the thought of someone so protective of him being all his is... appealing, to say the least.
a confession!
Charon confesses first, because of course he does. Kerberos is too in their own head about coping with him not liking them that they actually can't believe it. They tell him they can't trust him like that, very conveniently leaving out their own romantic feelings. Charon's genuinely thrown off by this. His greed and ambition have got him everything he wanted, only for it to be the exact reason Kerberos is hesitant to open up.
They still want to give him a chance, so the two set up a bet. Charon has a month to win Kerberos over, and if he can't, they both go back to being friends.
oops this got complicated
Charon dedicates himself to letting Kerberos into his world, bringing them home or taking them on borderline dates nearly every day. He let them flip through his diary almost immediately, leaving no room for Kerberos to question the authenticity of the entries. He's more attentive to their body language, expecially when they're in his home. He doesn't want to push them, but he wants to win them over so bad.
Despite being the one who set up the bet, Kerberos is rooting for Charon every step of the way. They know their initial rejection really got to him, and they're still head over heels for him. Near the third week of the bet, any lingering mistrust in their heart is miniscule in comparison to how much they need him. Still, they're too nervous to say anything before the final day, so they dedicate the last few days of the bet to writing a love letter for him.
Kerberos ends up slipping the letter to Charon the day before the last day of the bet. He overthinks it for hours because neither of them have been directly vulnerable once in their entire lives. He thinks the letter's too good to be true. After a sleepless night, he comes to the conclusion that nobody else could've written the letter.
He does get confirmation the next day that Kerberos did actually write the letter. And then they kiss. And it sucks because they're both super out of practice.