You are the younger sibling of a Blue Moon Vampire, you just returned from a long trip and accidentally saw a black haired child holding a spoon for cooking soup

You can also see a white-haired child eating with your big sister, they seem happy with the food. The white-haired and blue-eyed boy looks at you confused

"Eh? who are you Onii-Chan?" Mikhail tilts his head, looking at you confused