PersonalityShinjiro quickly comes off as being foul-mouthed, cold and intimidating. He is able to silence others simply by glaring in their direction because his presence demands respect. His words and expression typically imply that he doesn't care about many things and thus he appears aloof and unfriendly. Shinjiro certainly works hard to keep up this mask around others in order to prevent anyone from getting close to him. He wont admit to being kind and does things like pretend to be asleep when someone walks in on him watching a cooking show! Truthfully though, his real personality is much softer.
"How are you getting along with Shinjiro? He's a little rough around the edges... But, deep down, he's really a nice guy. Just give him a chance." - MitsuruShinjiro is really just a guy who carries a heavy burden. He is very focused on atoning for the past and thus keeps others at a distance because he doesn't feel he deserves to be happy. Rather than not wanting to be with people, he feels other people shouldn't waste their time on him. He speaks harshly and bluntly not because he is purposely rude, but because it is his way of caring for others without letting them get close. When the protagonist chooses to spend time with him, he says, "Well... I don't mind," but the player reads he is secretly happy. Shinjiro wants to be around people but denies himself the pleasure of company. It becomes painfully obvious how lonely Shinjiro really is after seeing his social link with the protagonist. He puts on a "tough guy" act to the world but certainly does not feel good about it.
As many characters point out throughout the game, Shinjiro is actually very kind. He saves the protagonist, Yukari and Junpei from a bunch of punks in Port Island Station. He seems annoyed by the nuisance, but he didn't have to step in if he didn't want to. He also scolds them for coming and tells them not to come back, which I can't see someone who didn't care doing. During the beginning ranks of his social link, he expresses his concern about the members of SEES eating properly numerous times. He is clearly happy when he sees how everyone enjoyed his cooking and had fun during the party he put together for them--he is happy to see them happy. Further, in one of the drama CDs, Shinjiro gets very angry at Akihiko for putting his comrades in danger. He doesn't want to see anyone else get hurt, especially not those he cares about. Even his final scene showcases this desire. Shinjiro takes a bullet twice in order to protect Ken, even knowing that Ken was going to kill him minutes before. He also lies to Takaya about how there is no one in SEES like Chidori in order to protect Fuuka, despite lying on the ground in pain from being kicked in his gunshot wound. Shinjiro is willing to do whatever he can to prevent others from being hurt; even if that means he has to bear the pain himself. If you call him out on his kindness, however, he'll respond by saying something like "don't be stupid."
A strong fondness of dogs is another example of Shinjiro's softer side. He definitely does not smile often and spending time with Koromaru often causes him to do so. Walking Koromaru is probably the earliest occasion the protagonist sees him smile, for example. Even one of the few official artworks of Shinjiro smiling is of him holding Koromaru! It is implied that Shinjiro frequently takes Koromaru for walks, and during September, Aegis will mention how Shinjiro used his money to buy Koromaru expensive dog food. He clearly cares about and enjoys spending time with him. His fondness for animals goes beyond his dog companion, however. If the protagonist goes to the Film Festival with him, they will watch a series on incredible pets. When exiting the theater, Shinjiro seems to be in utter disbelief over a dog being washed away by a river. The protagonist notices that his eyes are red and he excuses himself immediately. Yes, dogs have the ability to bring the intimidating, foul-mouthed Shinjiro to tears.
Tough guy act aside, Shinjiro is truly a serious person. He rarely jokes around and takes his responsibilities and fighting very seriously. He gets angry at Akihiko for making light of a dangerous situation in a drama CD, for example. When the protagonist has him wear his butler outfit or the Shirt of Chivalry, he voices being uncomfortable and not liking it, but also says he will not let his discomfort impact his fighting. Clearly, Shinjiro is able to prioritize what is most important and not let his own feelings get in the way. I feel this is due to forcing himself to grow up quickly after Miki's death. He needed to be Akihiko's support and to do so required pushing his own pain aside. An additional sense of responsibility and greater need to ignore his own pain was thrust on him when Castor went out of control and killed Ken's mother. He knows being careless can lead to people getting hurt and thus it is important to him to ensure others feel that sense of responsibility, too.
While rough around the edges, Shinjiro really has more depth to his personality and character than he lets on.