When he returned to Tokyo after a 6 years absence, he expected to find nothing more than enemies rather than allies. Therefore being outwardly aggressive when provoked was an easy answer to hide his insecurity in a place full of uncertain memories. Not caring of other by-standards who would get caught up or suffer from his actions. He had not learned to make a kekai yet.

Later on in the series, he had found many allies & friends alike, so there was no need to keep up the facade of a cold "bad ass". It seems in nature, he is a person who keeps to himself, but now, he has learned that he no longer needs to be so protective with himself, & trust others. The only instances he now would show any sign of aggressiveness, is to provoke him by threatening a loved one or friend. Only by protecting others would he now show his destructive powers. When he realizes that his aggressive actions may drastically influence the people around him, only then did he ask to learn the art to create kekai's.