Silence and calm is the charatcer of Gingetsu. After found Lan (Ran), he decided to live with him but of course it's not easy to get the permission from The Wizard. Since himself is the owner of two-leaf clover and Ran is three-leaf, if they combine their power The Wizard will sure cannot control them anymore. Gingetsu granted his life to The Wizard that they can kill him anytime if he try to do so. And that's the reason they let them stay together.
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