At first, he is a shy, taciturn and timid boy who doesn't stand out, but is always kind and nice to everyone. After he starts playing Vanguard, he starts to come out of his shell and appears more confident in himself, resulting in a boost on his Cardfight skills. During the regional tournament, he doubted his ability when Misaki wouldn't make it in time for most of the tournament, and again when he was paired up to fight Gouki in the finals, but through winning the team's first match, and some encouragement from Kai, he regained his confidence and grew determined to win.
After Aichi gains PSY Qualia, he begins to act very much like Ren Suzugamori; arrogant and obsessed with growing stronger, yet staying eerily polite throughout, which he frequently displayed once Ren gave him a Shadow Paladin deck, which appears to fuel his PSY Qualia. Aichi starts to doubt himself, but quickly get's over it after seeing his friends having fun during a shop tournament at Card Capital.
During Season 2, he displays more of his calm and determined personality while he was fighting with other fighters, even when he was in the brink of losing against Christopher Lo after the latter got PSY Qualia powers. However, he grows increasingly worried when his Royal Paladins were replaced by the Gold Paladins, and despreate for answers as to what happened. This starts to lessen after fighting with the new clan and learning to respect it. After facing fighters like Kourin and Jun, he begins to forge his own path, growing stronger with each fight. He refuses to leave his friends in trouble if he can help them, even when the circumstances dictate that it is a waste of valuable time, as shown when he accepted Christopher's rematch to try and break him out of his Psyqualia-induced madness, even when Cray and Earth were in danger.
In Season 3, it is shown that Aichi, outside of any Cardfight!! Vanguard-related event, is still quite unsure and nervous, but this side of him completely vanishes whenever he plays. He also starts to act more like a leader in the Cardfight Club. Naoki, Rekka, and Kourin have all noted that during their fights with him, he seems like a different person, only looking forward and having his sights set on winning.