Zaraki's surname comes from the district he once resided in, Zaraki, which is district #80 of the North Alley of Rukongai. District #80 is the worst, most lawless region of Rukongai, full of thieves and murderers (whereas area #1 is the most orderly and law-abiding). While residing in District #80, Kenpachi was nameless. During that time, he became proficient in swordsmanship and killed numerous enemies.
After some time had passed, Kenpachi found his way to the Seireitei. He defeated and killed the previous Captain of the 11th Division (whose identity is currently unknown) and gained his seat in the Gotei 13 in this manner.

Xanxus is the current Leader of the Varia, Vongola IX's adopted son, and the main antagonist of the Varia Arc. He was born into poverty with just his mentally ill mother. His mother discovered his Dying Will Flame when he was very young and brought him to Vongola IX. When she and Xanxus confronted the 9th, he took Xanxus and placed his scarf around him, agreeing that he was indeed his son even though he had never seen this woman nor her son before. During the Varia Arc, he and Tsuna battle for the Sky Vongola Ring and the position of the 10th Vongola Boss. Later, in the Future Arc, he remains the leader of the Varia and leads a raid against the Millefiore, taking their Headquarters. He battles against one of the Fake Funeral Wreaths as well and wins, showing that he has grown much stronger in the Future.

Xanxus