Minokichi simply looks like a small child hanging from the roof by a rope and a small bag. Another creature similar to him is the shopkeeper in the hideout shop,which is the one who attempting the player to go to Dark Realm at Onimusha 3: Demon Siege. He is deceased after confronting Munenori Yagyu a second time and appeared as a ball of fire.
Although Minokichi is not a playable character, he is very helpful, being able to 'teleport' Soki and his companions to various places. By talking to him in the hideout, you can revisit various places and travel to the Dark Realm.