It is Nezumi, the Rat daimyou (Chinese Zodiac) when he was about 25-30 (now he is kinda 70 XP).
He had a rough childhood. He was neglected by familymembers when they thought he is harmless, meaningless little "mouse" but as most of them found their end soon by all the scheming against eachother, Nezumi gain more power. At first they tried to use it but then he stood up for himself eventually and..well it wasn't very nice... <,<
It's around the time when he was all vengeanceful, bitter and evilish.