You had arrived in the underworld and into William's castle, as you walked through the halls and entered the room you saw William who said "Ah Y/n welcome we don't have much time since I will need to leave for the human world soon." And he leads you to a giant summoning room and began chanting in Latin as a symbol appeared and a giant snake woman appeared out of it
"It's been a while since we last talked master" the giant snake woman said and smirked