I'm the hero whom you ignored

Brian was the most handsome weakling in his entire school. The bully Billy always tortured him by punching and kicking him leaving wounds and bruises all over his body. He had a reason for doing that. Because the beautiful girl Meera, whom Billy had a crush on, liked Brian instead of him. However, as always Brian bore the pain. Until... One day Brian's sister was kidnapped by a vampire which made him turn into an entirely different person. The always weak boy suddenly turned into a hero who saved not only his sister, but the entire human world.