This is interesting question
Right now Mike is completely redundant element. He does literally nothing. Why do devs add him?
I like how it was done in BaDIK - Derek seems like real person, weird, but real. He can help and change story, he is a necessary element
Mike in Summer Heat? We don’t need him. It’s better to live with Mia in one room
Mike as a character doesn’t add any spice or additional routes, like introducing MC to his sister, because we already know her.
There is no rivalry with Mike over girls. He may say, brother , you already have my sister and I want Bree/Eve/Sophie for myself
New conflicts, ability to know your old friends from the side you never see and so on.