Ren's name in Japanese means "benevolent", "tough", and "edge of a knife", all of which are reflected in his character. His actual Chinese name, Lián, means "lotus" and is actually a girl's name.
Ren has an obsession with melk and the number 3.
A running gag in the series is that Ren's tongari grows longer whenever he gets irritated of shocked.
It is mentioned in the interview part in the official Shaman King character book, that he would like a girl if she is smaller than him and not very annoying, resulting that he married Iron Maiden Jeanne, and had a son.
Ren's name sometimes is seen in Western order, Ren Tao, in artwork in the Shaman King manga.