I dont understand how someone could be confused by that either lol
Erm, except I don't think he was 'pretending' to be meek and mature so much as hiding his feelings until he was in a safe place to express them. I don't see that he was pretending to be meek anywhere, and I don't think it's immature to hide your feelings in a work environment. That's pretty standard workplace etiquette.
He showed considerable restraint by waiting until they got into the private apartment, which is a sign of maturity, and he promised he wouldn't do anything Oikawa didn't like, which was not only mature, but reassuring. When Oikawa told him "show me your true self" I think he just meant to show him his true feelings because the revelation of thsoe feelings surprised him so much, they had been so well hidden. I don't think he was actually asking him to change his personality.
I agree with you :) wish there was more
Look at the top right panel:
http://www.mangago.me/read-manga/imitator/mh/c001/20/
The older guy himself says "meek".What JKST and Mushroom Sprouts said are both right.The guy is pretending to be meek(he acts like that for gaining Oikawa-san's attention,but in addition to that, it's just the way he conducts himself at work I guess, being the mature guy.It's not really uncommon, since there are many other manga where the seme has a dual-personality, one for others and the other exclusively for the uke).Satomi gets shocked and says "You realize?" when Oikawa-san asks to show him his true self, meaning that he was trying to act like a gentleman but his true nature/possessive side was revealed.Bottom right panel:
http://www.mangago.me/read-manga/imitator/mh/c001/25/
Oikawa-san is surprised that even though Satomi looks so calm and mature, he's a pretty aggressive and persuasive guy.Of course he wasn't asking him to change his personality,"Show me your true self" means that show me this possessive side of yours.In a way, he is asking him to reveal those hidden feelings of his that he's been hiding.
It's pretty easy to understand why they were confused, actually: the synopsis claimed the name of the son was Satomi. I'm pretty good at reading past errors but even that name tripped me up a bit and I had to reread a couple of pages to see how the son came into the equation at all.
If you weren't reading all that closely, it would be pretty easy to think both their names were Satomi and (since most mangaka don't have 2 characters with the same name) that they were the same person. But the end of the manga wasn't that well done anyway (too few pages left?)
TOO EVERYONE WHO IS CONFUSED!! This is NOT INCEST!! .. It's not his son.. When Oikawa told him "show me your true self" he was referring to the fact that the other guy was pretending to be meek and mature because that's what he thought would make oikawa like him... I'm not really sure how people got confused it was pretty obvious