exoskeleton
Mechanical attachments worn by a character, sometimes grafted directly onto their body. Depending on the amount of separation between the wearer and the exoskeleton, it may sometimes also qualify for the mecha tag. See post #5967547 and post #5387585 for exoskeletons that are also mecha, and post #5731043 and post #4515304 for examples that are not.
For organic exoskeletons use carapace.
For a type of weapons/armors in Kakugo no Susume, use Kyouka Gaikokkaku.