Trying to find a manhua/manhwa (not sure which one) that had a MC that was either reincarnated or isekaied into a world and was stuck in the world but people came into the world to complete a mission. He killed them and was able to travel to different world and also probably the point where his system activated. He complete missions while being able to use previous powers that he had gained. He is able to turn girls into cards that comes with a rarity. He is able to use the power the girls possesses through the card. He is also able to bring them along and hang around in some sort of subspace. Hope this description helps.