Our name (pronounced HAH-ree-sehn DIE-ko) is a language pun in two parts.
First, a harisen is a tightly folded paper fan which gets comedic use in Japanese media to correct the wayward by giving them a good, and audibly distinctive, swat. Second, we think of ourselves as devotees or fans of Taiko among many other geeky things.
The word Daiko is a modification of Taiko used to refer to drums, styles, and names of groups when Taiko would be used in a compound word or name like ours.
We are Harisen Daiko. Fans that hit things.
Wikipedia, in it’s infinite wisdom says this about “harisen”:
The harisen (ハリセン meaning “slapping fan” in Japanese) is a giant paper fan, usually made in a closed fashion. It is most traditionally used as part of a manzai act, in which the straight man (tsukkomi) smacks the funny man (boke) in response to their jokes or idiocy.
The site tvtropes.org has a slightly different take:
It’s just an ordinary, if large, paper fan — accordion-pleated white paper, taped at one end to form a handle. But some characters wield them the way others do the dreaded Hyperspace Mallet, and get much the same results — the unfortunate target usually goes rolling down the street from the force of the blow.