Yoru is Ikuto's cat-like Guardian Chara. You can say that he is Kiseki's sworn enemy (well they are enemies). He isn't around Ikuto all the time, and when he isn't he gets into lots of mischief and usually messes up Amu's day (most of the time), or sometimes he helps her out with some problems like finding out who had stolen her Guardian Eggs.
Yoru wants to help Ikuto find the Embryo but always fails. He can summon a cat army. He is much of a troublemaker and enjoys doing pranks on the other Guardian Charas. He helps Ikuto do Character Change. Together, they are the Black Lynx.