PersonalityOne of the first things I noticed about Akihiko's personality is how much confidence he has. The source of his confidence may change during his character development, but he certainly never appears worried about losing. Initially, I feel much of this confidence came from his one track mind about getting stronger. He needed to become stronger to feel like he was doing everything he could. If he was going to get stronger, he had to win. Therefore, losing was not an option. Pouring his soul into gaining strength was a defense mechanism for him, so I wouldn't be surprised if he unconsciously created a mental block on any scenario in which he would lose. In the 5th character drama CD, Akihiko is well aware that Death is on the floor with them and could turn up at any minute. Even so, he engages in battle with some Shadows on the way to regroup with the others. Shinjiro scolds him for doing something so dangerous and demands to know why he would do that. Because of his confidence and pride, however, Akihiko didn't feel the same way. He thought he'd have no problem taking the Shadows out and he simply "miscalculated" how much time it would take. Truthfully, Akihiko likely did not stop to consider the possibility things could go wrong before jumping into battle. He tends to be pretty impulsive at times.
Akihiko also gets a thrill from fighting! Anyone can tell he greatly enjoys a challenge and treats fighting Shadows almost like a game. I mean, how many people would be on the ground with broken ribs and still have eyes glimmering with excitement over the size of the Shadow they just got beat up by? Akihiko even considers wearing a disguise in order to get past Mitsuru and explore Tartarus with the others while he is injured. He really does not like "being out of the ring," so to speak. Considering how much effort and time Akihiko spent training, boxing and trying to make himself stronger, though, I'm really not surprised he has come to enjoy a good fight. His whole life is based around fighting, with the exception of school. His only mentioned "hobby" is boxing and his two magazine subscriptions are also about fighting. Long story short, fighting is an important part of his life.
A more subtle part of Akihiko's personality that generally shines through only when someone is in danger is his concern for other people. He knows what it feels like to lose someone and will do anything to prevent having those painful feelings again. Akihiko's motivation driving his desire to protect others stems from his past, but I do think his feelings are genuine. He clearly worries about the protagonist, Mitsuru and Shinjiro throughout the game, for example. Ultimately, he doesn't want to lose another person--especially not someone close to him. Akihiko will not take no for an answer when a person's safety is involved (except his own, I suppose). When the others seemed to give up on being able to rescue Fuuka safely, he has a sudden burst of anger that seems almost out of character for him at that point in the story. Akihiko says he will go rescue her himself if he has to because he won't give up on her if there is a chance to save her. Honestly, I truly believe he would have gone alone if no one else wanted to go. Akihiko has taken it upon himself to be a protector of sorts. At first, it was likely because he felt he failed to save his sister. However, when the protagonist helps Akihiko overcome his guilt, he resolves to protect everyone precious to him. A genuine concern for others remains a big part of his personality.
I would also argue Akihiko is a very mature character. He was designed to be cool and adult-like and I think the designers pulled that off well. Akihiko does not partake in frivolous activities and honestly just doesn't relate well to half the things Junpei says or does. While he can be childish at times (according to Shinji, he's just a big "crybaby"), he is almost always well put together, calm and seems to be wise beyond his years. The only times Akihiko's "childish" side comes out is when fighting or when he's dealing with his feelings around Miki's death. He is impulsive, rash and easily excitable when fighting and sometimes doesn't realize what consequences his actions have on others. In that sense I can see why Shinjiro sees "childish" behavior in him. The only times Akihiko is actually seen crying is after Shinjiro's death/coma and when talking to the protagonist about his guilt, though. But who can blame a guy for being overwhelmed by emotion in those situations? People in general tend to fall back on earlier developmental stages when experiencing high stress. Akihiko is able to pull himself together and focus on what is important during each of those moments. That, I think, shows true maturity.
While Akihiko is certainly mature in most aspects of his life, his ability to interact with and relate to girls is certainly far from refined. It's certainly amusing how awkward he is around the opposite sex and the game pokes fun at him multiple times for that. Upon closer inspection, however, I think Akihiko's trouble is not just because he is unsure how to behave around girls. His tendency to keep everyone at arm's length is a major contributing factor as well. After experiencing the devastating loss of his sister and recently strained relationship with Shinjiro, Akihiko thought it would be better to not let people become too important than to risk the chance of losing them. He wouldn't get hurt if he didn't make connections with people. Further, he'd be able to pour every part of him into getting stronger without being tied down by relationships. He was so focused on getting stronger and preventing those feelings, it was almost like he had tunnel vision. He didn't see or feel what others were expressing. Right from the beginning the player can see Akihiko is rather professional when interacting with the other characters. He seems close to Mitsuru and Shinjiro, but otherwise he does not put noticeable effort into bonding with anyone. With the help of the protagonist, Akihiko eventually realizes he was wrong by choosing to live that way and resolves to work hard to protect those he cares about instead. From that moment on, I'm sure Akihiko had much more satisfying relationships and was therefore able to interact and relate with people better.