Tensei Shitara Slime

A world full of magic, and various monsters. In the Middle Ages, the player's questions are always answered by the "system" (this is a voice in the players' head that only the players can hear, he answers briefly and in fact). There are many ruins of ancient settlements, kingdoms, monsters, magic, and dragons in this world. Over time, you can get various skills, but for them you need to fulfill certain conditions, for example, if you drink poison for several years, then over time you can get a poison resistance skill and the like. There are the most powerful creatures in this world, they are called "Demon Lords", there are only 9 such creatures in the world, they sometimes arrange meetings where they discuss their plans. To become a demon lord, you need to consume 10,000 living souls.