Melodiums

Melodiums are instruments wielded by all playable Ratatans, such as Keroronpa, Pyokorappa and Buttonda.
Out of all Ratatans shown so far, each one uses its own unique Melodiums. This makes for a total of 8 Melodiums types that have been seen so far.

Trivia

Cobuns were seen using their own versions of smaller Melodiumss in concept art. This was later changed to traditional weapons instead.