If you paid attention, all throughout Yukas chapter Masato was getting charmed and it was effective way before he was pinned down. After which he clearly didn't say no - he was all blooming red (read: aroused) - nor did he avoid all the subsequent kisses. You can't force a mouth to mouth kiss to an unwilling participant, it's simply not how it works.
He was successfully charmed and conquered - something people here have a hard time accepting (because of the implication).
Now, he was clearly way more aware of the dynamics at play by the time Seira had her run at him, that however doesn't take away from just how creepy Seiras approach was.
There was nothing cute about Seiras "expensive gifts in exchange for sex" transactional approach, she took like the worst possible strategy imaginable considering all the weapons in her arsenal. (and she has way more weapons in her arsenal than Yuka does, Yuka merely had the first mover advantage)
Seiras approach wasn't far off from random eager women on the street trying to hit on guys (a common occurance in this world) and offering money, which Masato has deflected plenty of by this point. There's just nothing cute and charming about that.
If this happened before Yukas arc, the outcome would very likely be similar.
Seira is simply not very good at piloting her body.
