Why They Aren’t Showing Up?
For Akinari, after you see him with Maiko during one of her early scenes, you then need to talk to him on the bench at the shrine behind the play equipment and he tells you about his missing red pen.
Then you will then find Konamaru with it on the first floor of the dorm under his paw. Take it and return it to him. That starts his social link.
For Mutatsu, if you have Yuko at rank four, just go talk to her and she tells you about him. You do not have to hang out with her after she tells you.
After that point, he will then start showing up on certain nights at the club.