Leon is a cynical, grumpy, and cold young man. This is because he was treated as an outcast at the Observatory due to being an orphan. He is rather blunt and is not very good with words or respect, especially when it comes to women. He was highly misogynistic due to an event from his past, but his attitude changed after meeting Violet, the first girl he has ever fallen for. His view of women also starts to change after meeting different women who work as an Auto Memories Doll. Meeting them made him realize that they weren't girls who were only after rich men, but women who were serious about their jobs and to convey people's feelings. He knows he's bad with women and initially disliked them, but he doesn't hate all of them and believes that there are good women in the world, such as Violet. He also has a bad habit of associating his mother who abandoned him with anything.

Although Leon has a rude way of speaking, he is actually a very caring, kind and helpful, albeit awkward, boy. As he doesn't want to admit having a soft side, he comes off as dishonest and does not want to admit his true feelings.

He is very passionate when it comes to astronomy, having been interested in it since childhood. As time went on, Leon began thinking about his own future and happiness, as he decided that instead of waiting at the observatory for his parents to return, he'd travel the world like Violet.