Michael (the Key) · Date a Slime

Mukuro's key also exists as an item, dateaslime:michael: it is what you hold when Michael is manifested. It isn't meant for hitting — every Michael technique goes through the skill's modes — but without it, nothing fires: Segva, Lataibu, Meteor and Deflection need it somewhere in your inventory.

Getting the key

The key can't be crafted, isn't found in any chest and isn't listed in any creative tab. It only appears through Michael's Manifestation mode: a black rift opens above you, the key spins down out of it and lands in your main hand. Whatever you were holding moves to your inventory, or drops if your inventory is full.

Pressing Manifestation again sends the key back: it vanishes from your inventory, wherever it was.

Mukuro holds it throughout her fight, but never drops it.

In hand

No damage bonus and no right-click use: a hit with the key counts as a bare-hand hit.
It doesn't stack (1 per slot) and is fire-resistant.
It is rendered with its real 3D model, star ring and bit included.
Segva on the ground drives it into the earth: it leaves your hands during the scene and comes back after about 10 s.

It never leaves its wielder

An Angel's manifestation isn't loot. The key is therefore guarded against every leak:

Throwing it: refused, it goes back into your inventory. If your inventory is full, it vanishes instead of dropping — just call it back.
Storing it: impossible in a chest, barrel, hopper, Shulker box, Ender chest, crafting table, the 2×2 grid or a mount's inventory; it is removed from any slot that isn't a player's. No bundles either.
Displaying it: item frames, armor stands, allays and decorated pots refuse it.
On the ground: a Michael key can't exist as a dropped item, by any route.
On death: it is removed before your inventory spills. Nothing to recover where you died: after respawning, one call brings it back.