Shin is the character most prominently placed in the artwork, which generally means that he's the closest thing to an official route and the one that probably gives the best feel for the game (i.e. the one you should play first). Helpfully, when the player is asked to choose a world, Heart is at the top of the list.
I played his route second, though I was a little doubtful I would like him because Shin looks rather taciturn.
In retrospect though, I can see why Shin should be played first, if one is inclined to do multiple playthroughs, as his route takes care to establish all of the main characters and the supporting cast.
As is common throughout each of the worlds, the other love interests still exist and have mostly the same personalities, but might occupy a slightly different space. For instance, Toma works at the maid and butler cafe along with the protagonist in Shin's world, but has stopped working there in his own.
Shin's story is surprising in that he figures out that the protagonist has amnesia almost immediately. While his is not the only route to do this, it's surprising considering he's the closest thing to a default and it throws out a game mechanic Orion lectures the player on in the prologue. But what this does is make his storyline significantly easier to get a normal or good ending with since the player has less parameters to juggle.
A player seriously has to work at torpedoing the relationship in order to get a bad ending. I was able to get normal even with my trust meter at zero because my affection was still too high.
Shin is not an easy character to picture as a boyfriend. He's blunt and has little use for sentimentality, but what's interesting is that he makes it clear that the protagonist gave just as much as she took. It's nice to know the protagonist was a spirited girl while she had her memories.
He's very problem-oriented, in that when he finds one, he methodically goes about what he needs to do to solve it, even if the methods might be considered questionable. For instance, he's an incredibly good liar, and while he never does it maliciously, he lies several times over the course of the storyline to get the information he needs, and he's uncomfortably deadpan about it.
His pragmatic nature also makes him eerily calm in situations when panic would be more appropriate, which leads to the main thrust of his storyline.
In this world the protagonist was in an accident where she fell down a cliff and Shin was initially suspected of pushing her off of it. Unfortunately, due to her memory loss, she can't remember what happened that night, but she's told that her pre-memory loss self had vigorously defended Shin, which resulted in him being released by the police. (She loses her memory a couple weeks after the accident.)
The beginning of Shin's storyline was all right, but with Shin being difficult to get along with, the story didn't take off for me until the second half, after Shin is brought in for questioning a second time. At this point, Shin reveals that there was something else that happened the night of her accident and that there may be a real culprit that isn't him.
Once he begins to set up the trap his story becomes a lot of fun, and I like that the protagonist recovering her memories is key not only to exonerating him, but to pinpointing the real culprit.
The plot also makes use of the fact that memories are not reliable, by having one memory that should not be possible because it contradicts known events, and unlocking what really happened is the only way to get the good ending.
Though always blunt, Shin mellows over the course of the story and reveals some of his own insecurities, including what it's like realizing that his relationship with the protagonist has vanished and left a stranger behind. Flashbacks as the protagonist recovers her memories also flesh out Shin's interesting brand of "tough love" and how it's actually helpful to her, because his no-nonsense critiques push her to do better.
The game does a fairly adequate job of narrowing down the suspect pool, though I admit I probably only got it right because I'd played Toma's route first, and if you have, you know enough about him to realize he would have a motivation. I don't think the game does enough to eliminate all the guess work though, and I was hesitant to blame Toma just because I wasn't sure how much overlap there was between worlds.
In the good and normal endings Shin piles on all the evidence that Toma is the culprit (not in pushing her off the cliff, but in a subsequent injury after finding her), mostly using information the player has already seen but not necessarily had any context for, with the final piece being the key memory the protagonist needed to remember.
Given Toma's route, I'm a little surprised the outcome was as mild as it was, but viewed strictly within the context of Shin's route, it was a satisfactory ending, and the interplay between the protagonist and Shin once she gets her memories back is pleasant. They do make a cute couple and I can see how their relationship works. She really does speak up and dishes out as much as she takes.
Overall, I'd say Shin's route was the sweetest and most fulfilling of the ones I played, though he does take some getting used to. His certainly was the most fun, as I loved the whole recreating the night of the crime to discover who the culprit was, and I found myself grinning at the monitor while the happy ending played.
I think it's really unlikely that anyone would get Shin's bad ending unintentionally, but in the event they do, it does foreshadow what Toma's route is going to be like. In a way, I wish some of that came out in the even good or normal endings just to give players better warning.