Scalemail

The Quirk followed the familiar path through All For One's hands: stolen from a person the story never names, kept in his collection, then gifted to a subordinate. Shuichi Iguchi is the recipient, receiving it in Chapter 371 and showing it off in the anime from Episode 152.

Its title points at scale armor, the historical style of protection built from small overlapping plates sewn onto a backing. The concept has a close cousin within the series in Scales, since both wrap the user in a shell made of the same basic form.

The Quirk also carries a note of finality. Before All For One dies, the final pair of titled abilities he is ever depicted handing to a subordinate consists of this one and Body Bulk.

Triggering the ability layers hard, sharp-edged plating across the body. The benefit runs in two directions at once: the wearer becomes markedly tougher to injure and noticeably stronger. The anime renders the plating in a deep red.

The armor arrives at a cost. Each scale forces its way up through the flesh, tearing the skin and leaving the user bleeding as the shell forms. Protection is also finite. Sufficient force cracks the plating outright, which Mezo Shoji proved by pulverizing most of Shuichi's shell with Octospansion before Present Mic's Voice finished the job.

Whether those flaws are inherent or simply the result of a mismatched host is an open question. Nobody but a secondhand owner has ever been seen using it, so the original holder's experience of the Quirk remains unknown.

Shuichi Iguchi is the only person shown fighting with Scalemail, using it as battlefield armor during his clashes with the heroes.

All For One held the Quirk before him and counts as a former owner, though he transferred it rather than deploying it himself. The unnamed individual he took it from is acknowledged but never depicted.