Have Juiro Brave Rush and kill all the little death things, then up his attack and use his super mover (Brave Dash) on the final Boss. It should be a one hit kill. If not, hit the Boss again with normal attacks. You should win in about two or three minutes, depending on your level.
In-Game History
Open menu (press square) and go to "System", click "Load Vol.1 Data", load your data from "The Legend of Heroes: A Tear of Vermillion" and you will unlock some events on your "History".