That's the question, after a night in which Inoda has fucked her in all possitions which the only explanation of her lewd, what rests? BJ, anal, public sex, maybe a rusty trumpet, and bye Kirito. IMO it's not a very hard way of corruption, from the first scene of the second part we can see that Asuna can't be satisfied by Kirito and she is remembering that night all time meanwhile she is masturbating herself. Simply she has an affair or she is right in love with Inoda. I would see better to show a gradual corruption beggining with just a sexual encounter with Inoda as an accident, or unwilling act. I understand that people can be happy with the evolution to anal, it's ok, but I would prefer more resistance, more contradictions in Asuna's mind, an opportunity to come back to Kirito. The beggining of the second part makes impossible the relationship with Kirito.