Board Thread:General Discussion/@comment-32898414-20170821062018

Does anyone know what the name is for the shoulder guard / short sleeve thingy is that some of the guys wear under their shirts? Mutsunokami-kun has one,  Munechika-sama does, and then Kogitsunemaru, Urashima, and Nagasone all have ones that look a little more substantial (as illustrated in the official art book). I'm just curious what the official term is (maybe a Japanese word?) for it and what they would typically be made from. 