nineball

The Armored Core (AC) piloted by Hustler One and the main antagonist of Armored Core and Armored Core: Master of Arena, often spelled "Nine-Ball". It is considered one of the strongest and most iconic ACs, due to its status in-game.

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, created by and protects Raven's Nest system.

Nine-Ball=Seraph is an upgraded version in Master of Arena and most common depiction.
Nine-Ball Onyx, referred to as Nine-Ball or Baby's Breath in-game, is a recreation of the original Nine-Ball in Nine Breaker and Nexus.

Nine-ball is a recurring element in the series and appears or is referenced in most games, often by association to number 9. References include, but not limited to: White Glint's pilot and V.IV Rusty being ranked 9th in their respective games or HAL 826's coloration and the shape of its head in VI: Fires of Rubicon.

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