the act of a first kiss itself means nothing to masayoshi, he canonically spent so little time thinking about romantic love he had to have an epiphany about it. BUT, in the miniscule amount of time he dedicated to considering the subject, he absolutely decided that if he were to ever share a first kiss, it would have to be meaningfully timed, like in a show. a big kiss of gratitude, right after a narratively satisfying romantic moment...
of course, goto, who had comparably more normal ideas on romance ("comparably" is doing a lot of legwork there), would feel somewhat slighted by the fact that masayoshi never seems interested in "sealing the deal", as it were. so imagine his surprise after a tense battle, he runs up to masayoshi to call him an idiot and check for injuries as usual, and masayoshi asks, in a quiet voice "why haven't you given me a kiss yet?"
now angry that he realizes they BOTH were waiting on each other to do it, he fucking rips masayoshi's helmet off and plants the world's biggest one on him
(it becomes a common practice afterwards)