Finger Bearers are a type of Cursed Spirit that have become a special grade after devouring one of Sukuna's Fingers.
Finger Bearers begin as cursed wombs where they gestate until birth. During this period they can be seen by non-sorcerers. Once born they create an Innate Domain, a precursor to a Domain Expansion, that warps the dimensions of its birthplace.
Finger Bearers possess the normal abilities of a cursed spirit but they are incredibly powerful due to possessing one of Sukuna's Fingers. So far they are shown to be intelligent cursed spirits with a perchance for cruelty and toying with their opponents, much like Sukuna himself.
Finger Bearers act like regular curses and tend to linger at their point of origin and attacking any individual that enters their domain. They also possess incredible amounts of cursed energy, being able to fire it out in unrefined blasts and even barriers.
However, despite their strength, they seem to lack any form of cursed technique and pale in power when compared to Sukuna.
Cursed Womb Arc
During the mission to confirm and rescue any possible survivors at the Eishu Juvenile Detention Center, Yuji and Megumi encounter a Finger Bearer that was born from the previously reported cursed womb. The spirit slices Itadori's left hand off before the boy attempts to buy time for Fushiguro to rescue Kugisaki. Once Megumi and Nobara are out of the center, Yuji switches with Sukuna. The King of Curses initially attempts to cooperate with the Finger Bearer, but the cursed spirit attempts to kill him, only to get completely overpowered. Sukuna is somewhat amused by the special grade's efforts, but in the end he activates his Domain Expansion: Malevolent Shrine and exorcises the Finger Bearer, taking his finger afterwards.