Osamu is Jaden's childhood friend whom he played Duel Monsters with while his parents were busy working. (In the Japanese version, Jaden calls him “Onii-san” which translates into “big brother”, in this case a term of affection, which is one way to use it.) One day, after Jaden lost to Osamu, he grew upset over the fact he couldn’t summon his favorite card Yubel in the duel. Osamu thought he was overreacting and tried to comfort Jaden, but ended up evoking the wrath of Yubel by accidentally insulting her. He went into a coma and was transported to the hospital. When Jaden went to see him again, Yubel inflicted further pain on him.
Deck
It is unknown exactly what sort of deck Osamu plays, however judging from the cards he is seen using it is most likely a Zombie Deck.
