He claims to be japanese even though his accent and blue eyes suggest otherwise. He tells Mugen, Jin, and Fuu his name is "Jouji". He says he will return Jin's sword if he gives him a tour of Edo, Jin agrees. However, it becomes apparent that he knows more about Edo than all of the other characters combined.
Isaac is part of the famous Dutch East India company, the Governor-General in charge of trade. Isaac was to meet with the shogun but instead wanted to see Edo instead, his subordinates had been delaying the meeting while looking for him. Fuu asks him if he's seen "The Samurai who Smells of Sunflowers" and shows him her trinket. After Examining it he says to never show it to people and that it's dangerous to be showing it around at all in Japan.
