I saw this coming from a mile away... especially after finding out the senpai was a masochist. I guess his friend is the only reasonable route left, unless a new girl shows up and becomes the princess he's looking for.
Well the sister would be great too but let's be real, incest never happens unless it's the main plot point. And personally I do like the senpai, but she's definitely not getting anywhere either since MC isn't into her for some reason.