This must be the answer.

During his time here, he's had to put up with tiny reminders about his brother's death. Klados, the profiles, Dazai's questions at the trial, and finally the the circumstances of his death. Every little reminder and mistake came crashing down on him, and now he's left with a sense of self loathing. He no longer believes or tells anyone he's a pair of twins that became one, but he does properly mourn his brother's loss in private. In the long run, he tries not to let his brother's death stop him from moving on with his life.

Hyoubu's pep talk struck a cord with him, and made him wonder why he blindly accepted Danny's offer and sacrificed himself for a chance to spite the Lady. After all that's happened, he's more likely to question things that seem too good to be true. He does not like being manipulated and after nearly becoming a Void he's come to fear losing his sentience... Or worse, his entire soul.

After all of the lady's manipulation, Shin's developed a vengeful streak. He still has no qualms about killing for his art, but he's also likely to target those who he believes have gravely wronged or betrayed him. He happily draws up blueprints for multiple designs he can work his enemies into and bides his time until he has a chance to strike. If he has a chance to strike. He realizes he can't count on being able to murder his enemies, so he's fine if someone else inflicts karma first.

Shin's picked up painting as a hobby. He prefers to paint portraits, the subjects ranging from seemingly normal to deeply disturbing depending on his mood at the time of painting. It's a fine creative outlet to tide him over, and he'll occasionally take commissions for small things, but it just doesn't hold a candle to his true passion.

Shin doesn't suffer from horror hunger anymore, but he did end up acquiring a taste for vegetables because of it. Not that he has any qualms with eating meat, he just got too used to the herbivore life. Occasionally he'll try to eat a live plant out of habit, but he is content with normal food most of the time.

After everything that's happened, Shin is painfully aware he's missing at least half of his soul. While this is alarming as an In-Birth, one who survived a Void attack with their sanity in tact and got supernatural powers in return, but for a while he was suffering through a partial transformation into a Void himself. While it's a blessing that condition was mostly reversed with the closing of the Hollow Night, what are the chances his past will haunt him again?

We'll describe some of his physical state in Twilight and much of his time in the Day for the sake of reference. Like most of those unfortunate enough to get trapped in Twilight, Shin had a crest where he was fatally stabbed. The appearance of the crest varied from person to person; In Shin's case, it looked a lot like someone smashed his body in and it cracked like fine pottery. The crest was very dark in Twilight, but started to fade once he made it to the Day.

More concerning to him and others were the signs of his transformation. The most obvious trait was a pair of webbed frills growing out from his elbows, semi translucent and dark blue/purple in color. They weren't too useful for flight, and he had to keep them moisturized if he didn't want them to dry out and crack painfully. A rather inconvenient addition, but he could easily hide them under his oversized sleeves if he needed to.

The most mentally scarring aspect of his curse was the hunger. He was plagued with a ravenous appetite normal food could not satisfy. His body craved life energy known as EXs, which meant he had to constantly feed on living beings... Not that there were too many of those in Twilight and he was being monitored by Wagner and his peers, which drove him to develop a habit of eating live plants. Yep, you read that right. Any plant that was even remotely edible, even from bushes and weeds. If he ever had to suffer through something like that again, he'd immediately assume the worst.

Shin is able to summon a doppelganger of himself at will. Although this ability should have gotten stronger upon the end of the Hollow Night and his escape from that world, Shin willingly limits himself for fear of losing what's left of his humanity.

As such, the limits of his powers are much like how they were in game: