Defeating Koishi Komeiji in version 1.0.4 grants the "Eye of the Mind" accessory. This item is essential for late-game progression as it allows players to see hidden traps in the Deep Cavern levels that follow. Additionally, you will earn a high-tier drop of Subterranean Ore, used for crafting the endgame "Abyssal Voyager" gear.
Koishi Komeiji's Defeat: A Complete Guide to the Cave Adventure v1.0.4 Boss Encounter
The "Glimmering Miner" set provides a 10% boost to dodge distance, which is crucial for clearing the Id Ego Burst radius.