This brash, arrogant youth is the pupil of In'ei, founder of the Houzouin Style of Polearm Arts. The style uses a cross-shaped polearm, which looks like a trident. Various accounts have him fighting with Miyamoto Musashi 宮本武蔵, but, mostly that seems to come from modern popular fiction.
It is no surprise, then, that Inshun is pitted against Musashi in this game. Musashi has been asked by Houzouin In'ei 宝蔵院胤栄 to knock the young man off his high horse. He does so, but when his name is announced as Kiryuu Kazumanosuke and not Miyamoto Musashi, Inshun refuses to fight him.
Musashi taunts Inshun, saying that he should humbly bear in mind that there are others better than him all over the world. "And you would be one of those 'others?'" Inshun asks. Then, he agrees to fight. Upon losing, he goes wild, throwing a tantrum, falling to the floor, and punching and kicking at nothing.