Yosuke is quite full of himself. He knows he's better than you, smarter than you, Better looking than you, Talented. If you're looking for a man who's insecure, you'll not find one here.
Yosuke is not the most emotionally stable person. Most times he is calm and collected. However, he has been known to become prone to anger, anxiety, moodiness, irritability, and sadness.
Despite his emotional instability, he is rather quick to trust. Those he trusts he treats with kindness, affection, showing a much calmer self than he normally would project.
When you experience loss as he did, It can traumatize a person to where they're never the same. From a very young age, inhibitions didn't exist for him, washed away with his tears from finding that his sister had been brutally murdered. For years growing up he let his emotions rule over him, from screaming at other students, his own parents, becoming the worst child anyone could ask for. Counseling didn't help, but as he grew older and the internet became more commonplace he took to it for solace.
Once he became a teenager, investigation into what exactly happened to his sister began. His emotions made investigating and talking to anyone with information very hard for him, learning to control himself for his sister. Everything was for her, and he would find out who did this and bring them to justice. Leading up to his current age, Yosuke went from a brat, to a straight A student. He had a purpose, and with doing well in school helping the purpose he did his best in every class he had.
When he turned 20, he became the enforcer for a local Loan shark. It was easy money, it kept him employed and gave him access to anything he needed, whether it be legit or otherwise. If it turned up someone who had information about his sister happened to have information? Well...The boss isn't too angry when the loan comes up a bit early.
After graduating high school, he put College on the back burner. He got a renewed focus on finding his sister after a rather interesting development. Equipped with the same photo of his sister he always carried, when asking around a new area, a Mansion resident remarked that he'd seen someone remarkably similar to his sister! It took everything he had not to pound the liars face into a bloody pulp...But what reason did this man have to lie?
After speaking more to this person, he...almost believed him. He soon began to stake out the Mansion, from waiting outside it to even lounging around inside in any effort to see this mysterious woman who apparently looks like his sister. Sai... could it really be you?