He is the last to join(return) to SEES but the first one to be gone or that's the impression about him if we play as the male MC
But, if we establish his social link as the female MC, we get to know more about his character and background stories.
What's more, we can see him with various facial expression that we never see before.
During the first few ranks, he acts like a big brother, constantly worrying about lots of things, like whether if Akihiko is slacking off during the fight, does everyone eat properly and so, whenever they spend time eating, he managed to make the MC gobble up everything without anything remain on the plate with his hard staring XD He even goes to encourage the MC to be tough because she is the leader.
Then, it's obvious that Shinjirou has deep affection for MC and he couldn't really say "no" to her, especially when it's decided that they will have a food party in the dorm and Shinjirou will be the one cooking the foods, though he seems reluctant at first, after some encouragement from the MC's part, he just goes, "alright, alright, I'll do it. Happy?" XD and during the party, when the others especially MC praising the food is delicious, he'll just blushed madly :D
But at the last few ranks, the scenes with him turned more serious. He obviously like the MC very much but he knows that his time is nearly up because of the repressant drugs he keeps taking to control his Persona which cost him his health and so, tries with all his might to push the MC away from him by telling her, she should hang out more with the rest and not to get too close to him. One time, he just sits while the MC do all the talking as he says he wants to hear the MC's story, so the MC told him about everything that has been happening around her. He then mentions about losing a pocket-watch. If you are able to find it, that's already a guarantee to complete his S.link.
When you showed him the pocket-watch, he gives it back to you saying that he thinks the pocket-watch suits you. Then it gets a bit gay, he told you to take care of Akihiko for him because he is an idiot and he told you the fight he has with Akihiko when they're children.
Afterward, he told the MC," because you're here, I don't have any worries" Right until here, the S.link will be MAX
If you want to have the "special relationship", you can still talk to him on the other night. First, he just told you that he's alright and talking to you makes him feel more at ease. Then, again he told you not to hang-out with him because he can't do/give
anything to you and keeps complaining why you choose to be with him. There's two choice of answers, "I want talk with you more" and the scene will end right away or "because I like Senpai" then it triggers another long scene with him and besides, it's nice looking at him all blushing and flustering because of the confession XD He first reacts by telling you not to joke but of course you have to convince him that you are not and he blushed more XD Then you could ask him whether to come to the MC's room or his. If you choose to ask him to come to MC's room, he says,"No way, we are not married couple and there will be misunderstanding" XD and that leaves his room, and again he says, "no way, I'm not a gentleman and it's not a room that you can enter" If you insist to, he'll again say "NO" and tell you that you should take care of yourself and not to care about him.
But then it says, you just ignore him and make your way to his room XD
Well, he just goes, "okay, you've seen the room, satisfied?" and complains that you are so stubborn, to ignore his wishes and intentions and then.... he says he'll do it too then goes to hug the MC without warning :D
He then says that he really can't help to fall in love with the MC, awake or asleep, all he ever see is she even though it's not supposed to be this way. You can choose to leave his room, if you refuse to leave, he says you are a "naughty girl"( that's how I interpret his words) XD and says again "Just so you know, I'm unstoppable" and you spend a longggg time with him XD
Then, right when he was shot by Takaya, he told the MC not to cry and obviously, this scene will only happen if you MAX his S.link and you are the female MC.
Sadly, this is the last interaction with him because even though he survived the shot, he remained coma for the rest of the game T_T
Aahhh..... this is very touching..