nineball

The Armored Core (AC) piloted by Hustler One, the main antagonist of Armored Core and Armored Core: Master of Arena, it is considered one of the strongest ACs. During the events of Armored Core and Masters of Arena it is revealed there are multiple Nine-balls and Hustler One is actually an AI controlling them.
Nine-ball is a recurring element in the series and appears or is referenced in most games.
Nine-Ball=Seraph is an upgraded version and most common depiction.

It is sometimes associated with Cirno from Touhou due to its status as the strongest AC and connection to the number 9.
Nineball=Cirno is a fusion of the two, generally depicted as Cirno with Nine-ball's color scheme and boosters.