In Love With A Vampire (Len X Rinto)
There was a forest that was said to have a mansion. The owner of said mansion is a vampire. Anyone who entered the forest, never made it back alive. Or so they thought.
Rin Kagamine had gone in the forest and came back an hour or two later. A few days later, she got sick. Her brother, Len Kagamine, got curious of the forest. How come only his sister made it back from that forest that everyone else never came back from? He had to find out.
So he began walking into the forest.