Shingetsutan Tsukihime

Synopsis

Shiki, in pain due to his wound, is watched by Akiha through the night. The following day, Kohaku reveals that the Tohno family carries inhuman characteristics, and the one with those characteristics designated the head of the family. With Akiha absent, Hisui allows Shiki into Akiha's study, where he finds a key. Trying doors throughout the house, he manages to open one that leads to a dungeon cell with "Help Me" scrawled on the walls in blood. Running outside, he recalls how there was another boy in his childhood also named Shiki and how he had killed him. Akiha, furious at him discovering this knowledge, reprimands Hisui and Kohaku.

(Source: Wikipedia)