Zen is calm and silent. He is overprotective of Rei and loses his collected facade when she is in danger, going so far as to threaten Teddie with his crossbows when he believes he is insulting her. Most of the others treat Zen's dedication toward Rei as mutually platonic, taking it as a given that they are in a friendship. Teddie, in contrast, compares the protectiveness to a father/daughter relation, saying that it is often heart-wrenching for a father to see his daughter grow up so quickly. However, neither dynamic is confirmed or denied by Zen himself. Despite ultimately wishing for Rei's happiness, he is willing to sacrifice it for her greater good.