Kojirou Sasaki

Kojirou Sasaki is a famous swordsman from Japan, known as the "History's Greatest Loser."

He is the winner of the third round of Ragnarok and the first human to kill a god, Poseidon, the most fearsome god of all, by cutting him into pieces. Kojiro used the third round as a chance to evolve his swordsmanship even further.
(Source: Shuumatsu no Valkyrie: Record of Ragnarok Wiki)