This is a custom HM worn by Muff McTomin, one of the 13. It's pronounced Atoll Five. It's equipped with an Auger round binder on the right arm, a Bash binder on the left arm, an Ashra Temple circus binder on the back, and a Grun long spear (all of the armaments are replicas). The buster launcher is optional. Apparently, it's called Five because it's based on Atoll. McTomin also says that it would have been perfect if it had a booster for the stack (L-Gaim Mk-II) on the back.
Nagano's plan for "heavy metal armor to be interchangeable" wasn't reflected in the series, so Nagano deliberately designed it himself. The name comes from the aforementioned rock band, but since they had released four albums at the time of broadcast, it also conveys the desire for a fifth album.