Monkasei is a fictional character in Soul Blade. He is only playable if a cheat device is used. He does not have a storyline, or an ending, but he makes an appearance in both of Hwang's endings, from that it can be assumed he is another student of Seong Han Myeong. He will use Hwang's attacks while fighting.
He is killed by the now evil Hwang, during Hwang's "Bad Ending" - seeing as neither Hwang's endings are canon, it can be assumed that Monkasei is still alive, that is assuming he actually exists in the Soul universe (he is never mentioned after Soul Blade, and doesn't seem to effect anything.)