CFV headcanon:
Aichi still has the Shadow Paladin deck. Occasionally he breaks it out to fight against Ren. He has a sadistic streak as much as Ren does when it comes to taking down strong fighters(it’s just that Ren fully adopts that persona for fights, Aichi does not)
The trash talk between the two during those kinds of fights is exactly how you think it’d be, i.e border line suggestive among other things(and despite constantly going on about how they’re going to crush the other and what not, there’s no real ill will between them and they’re back to normal as soon as they’re done fighting).
The first time it happened Kai almost had a heart attack. He thought the Psyqualia bs was back. Aichi and Ren maaay have enjoyed freaking him out a bit much.