Batman: Soul of the Dragon

In Bruce Wayne's younger years, while training himself to become a vigilante crime-fighter, he travels to Nanda Parbat, a secret monastery in the Hindu Kush Himalayan region, where he meets its caretaker, O-Sensei, and five other students training in the martial arts; Shiva, Richard Dragon, Jade, Ben Turner and Rip Jagger. O-Sensei eventually entrusts Shiva with Soul Breaker, a Muramasa sword in his possession, but otherwise remains secretive about a certain door at the monastery's outer perimeter. One night, Rip penetrates the forbidden door and kills Jade with Soul Breaker, which is the key to a mystical gate O-Sensei was guarding. This gate opens to the home dimension of the serpent god Nāga; four of his servants emerge and devour Rip before turning on O-Sensei and his students. Bruce and the others kill the demons, but to close the gate, O-Sensei sacrifices himself by entering Nāga's realm. The chamber then collapses, leaving only the gate intact.