The Slime Key is required to spawn the Demon Lord boss on Slime Island in Sailor Piece. This key unlocks access to one of the most important bosses for mid-game progression, dropping materials needed for the Rimuru Sword and Ascension. Getting the Slime Key requires completing a quest and farming specific enemies for crafting materials. Here's how to get the Slime Key in Sailor Piece.

How to Unlock Slime Key Crafting?

Travel to Slime Island through any teleporter on the map. Open the teleporter menu and scroll down to find the Slime Island option. Select it to teleport directly to the island. Head to the center of town once you arrive. Look for the Slime Key Crafter NPC. This NPC is essential for getting Slime Keys. Talk to the Slime Key Crafter for the first time. He will give you a quest to collect 7 Slime Pieces scattered around Slime Island. You cannot skip this quest or craft Slime Keys until you complete it.

Find all 7 Slime Pieces across Slime Island. These pieces spawn in fixed locations around the map. Search the island thoroughly to collect each piece. Once you have all 7 pieces, return to the Slime Key Crafter and turn in the quest. After completing the quest, the Slime Key Crafter unlocks the ability to craft Slime Keys. You can now trade materials with him to create keys for spawning the Demon Lord boss.

How to Farm Slime Shards

Go to the west side of Slime Island after unlocking the crafting ability. You'll find a group of Slime Warriors spawning in this area. These enemies are the only source of Slime Shards in the game. Defeat Slime Warriors repeatedly to farm Slime Shards. Each Slime Warrior has a chance to drop a Slime Shard when killed. The drop rate isn't guaranteed, so you'll need to kill many Slime Warriors before collecting enough shards.

Each Slime Key requires 2 Slime Shards to craft. If you plan to fight the Demon Lord boss multiple times, farm extra shards in bulk. Collect 10-20 Slime Shards in one grinding session so you can craft 5-10 keys without returning to farm again.

How to Craft the Slime Key

Return to the Slime Key Crafter NPC in the center of town once you have at least 2 Slime Shards. Make sure you've already completed the 7 Slime Pieces quest, or he won't offer the crafting option. Talk to the Slime Key Crafter and select the crafting menu. He will show you the recipe for the Slime Key, which requires 2 Slime Shards per key. Confirm the craft if you have enough materials.

Craft multiple Slime Keys at once if you have extra Slime Shards. Having several keys ready saves time because you won't need to stop farming the boss to collect more shards. Stack 5-10 keys before starting your boss grinding session.

How to Use the Slime Key

Head to the coliseum at the back of Slime Island after crafting your Slime Key. The coliseum is located behind the main town area and is easy to spot from a distance. Look for the Slime Summoner NPC standing just to the left of the entrance. This NPC handles boss spawning and requires a Slime Key to summon the Demon Lord. Talk to the Slime Summoner and select the option to spawn the boss. Hand over 1 Slime Key from your inventory. The Demon Lord boss spawns immediately.

Fight the Demon Lord boss to receive random drops, including Slime Core, Slime Remnant, Tempest Seal, and Sage Pulse. These materials are required for crafting the Rimuru Sword and progressing through Ascensions. For more guides, check the Sailor Piece wiki.