The nakago (pronounced nah-kah-go) is the part of the blade you never see: the unsharpened tang that runs down inside the handle. Forged as one continuous piece with the blade, it is the buried foundation on which the entire sword is built. The name simply means the “core” or innermost part, and that is its job, to be the structural heart hidden under the rayskin and cord.
Why the hidden part is the important part
Everything you can see, the guard, the grip ornaments, the lacquered scabbard, hangs off the nakago. A full-length tang that reaches almost to the butt of the handle is what makes a katana safe to swing; it spreads the shock of a cut through the whole grip instead of one weak point. The tang is held in place not by glue but by one or two small bamboo pegs, the mekugi, passed through matching holes called mekugi-ana. Pull those pegs and the whole blade slides free, which is exactly how you inspect what you are buying.
How to read a tang
Slide the handle off and look. A trustworthy nakago is a single solid bar of the same steel as the blade, often left with a deliberate file pattern and a darkened, honest finish. The file marks (yasurime) and the shape of the tang’s end are part of a smith’s fingerprint. The danger sign is a “rat-tail” tang, a thin welded rod bolted on rather than forged through, which is the classic weak point of a decorative wall-hanger. Near the end of the tang you will often find the smith’s signature, the mei, chiselled into the steel.
Why it matters to you
If you intend to cut with your sword, the tang is the one feature you cannot compromise on. Insist on a full, forged-through nakago, the standard on any honest battle-ready katana, and a sound choice even for a first beginner katana. See how the core is forged in how a blade is forged, or return to the full katana anatomy guide.