Curate, connect, and discover
as kids, i imagine kain got in a lot of trouble. all three of them were little trouble makers, (i mean, c'mon. three kids running around a castle? they're bored.) but only kain ever got in trouble. it seemed obvious to the king and rosa's parents and cid (and basically all of the adults in their life) that kain coerced them into spending their time making mischief rather than dutifully training as they should've been.
obviously, this was not the case. have you met rosa? that girl was out and about as soon as she heard cecil and kain might've been exiled from baron. she headed straight for damcyan, even though her lack of experience with heat had her ill almost instantly. rosa acts first and thinks later- if she wanted to sneak out to the town during training, she was the one begging kain and cecil to help her.
and cecil, despite his almost-inability to actually tell someone "no", generally went along with it. he noticed early on that kain was taking the brunt of the blame, and tried to take some himself, but between kain's self sacrificial nature and the king of baron's favouritism, cecil's attempts never held any water.
when cid returns with the enterprise to save everyone, he doesn't say a word to kain. he mostly talked to rosa and cecil, but he says *something* to rydia, addressing her presence. he says absolutely nothing to kain.
coincidence or not, cid sacrifices himself not a moment later with that bomb. coincidence or not, cid was their guardian- a consistent prescence in all three of the knight's lives. to avoid addressing kain at all? as if kain hadn't provided them with valuable information of the underworld at all, as if he hadn't shown his sorrow. as if kain hadn't repented enough for cid.
personally, i think that's part of why his mental barriers were weakened, and he couldn't repluse the "mind control" later on.
how awful do you think cecil felt when kain disappeared in mist? after accidentally annihilating an entire village, the guilt was already flooding in, let alone when he realized he personally dealt with rydia's mother. then the one person he had in the moment to rely on slides away in an earthquake that he definitely also could blame himself for (this is the most anxiety ridden man i've ever seen. he most definitely blames himself for that.) and is left with rydia, whom he dutifully takes care of, even though she hates him with all her guts (at the time).
imagine the self loathing, thinking that he condemned someone he loved to a death between stone and ash, thinking he could have prevented all of it if he'd simply had the guts to tell the king of baron "no". or investigated the ring he'd been instructed to deliver further. or anything else. but he didn't have time to dwell on it, because he needed to protect rydia, and that was his fault too.
i bet rosa hated. (hated!) being treated like she was weak, for being a white mage. that she spent her teenage years proud and ready to serve, just like cecil and kain, but was always shunted to the backline and protected, despite the fact that she could protect herself. that being kidnapped by golbez and being forced to be a damsel in distress drove her insane. that she wanted to protect cecil and kain just as much as they wanted to protect her- maybe even more.
i imagine for christmas that kain and cecil have a hard time with gifts. not giving gifts, but being able to accept them from each other (and rosa). like, they'd be those people that are like, "oh, no, don't get me anything this year," or "i'll just be happy with seeing you," which are nice sentiments and all, but rosa's love language is absolutely gift-giving (and acts of service, but that's a different comversation).
so eventually they have to have some sort of conversation that's like "you deserve gifts, i want to get you gifts, i don't feel pressured to get you gifts, i want you to appreciate them, etc. etc." and yknow im just thinking about that