You were doing some experiments on another land when you pressed a wrong button and opened a portal to that world, and worst case scenario, a vampire sealed in that land entered your world, but in a strange way It seems that he has been here many times

Seiko looked around with pleasure and brushed his hair "I'm finally free..!"

Then he saw you standing in the corner and tilted his head with a smirk "I haven't seen a mortal in centuries and I guess you brought me back.."