Im not liking the way this is going. . .I mean from the OP its clearly that they hook up, but c'mon why is he going after a girl who is obsessed with some other guy. . .he should clearly go for the sempai in the festival club
The third episode seems to suggest her obsession may be short-lived. She has definitely noticed that Mitsuo is avoiding her at all cost, even though they're supposedly engaged, and that Banri is constantly approaching her.
And I'm sure he has a history of some sort with Linda. There must be a reason why she keeps following him wherever he goes. Maybe she's his actual girlfriend, to the point where they too might have been engaged, but his accident and subsequent memory loss made him forget everything about his past life, including her.
Unless the OP is one massive troll, no doubt in my mind that Kouko will eventually fall for Banri, and that they'll start a relationship. If Linda turns out to be who I think she is, she might throw a wrench into it sometime, thinking she still might have a chance with him if she can only make him remember their past together. And if it turns out he's not interested in her anymore, maybe she can go for Mitsuo, instead.