This is the first Armored Core video game series where it does not feature the ability to purchase AC parts in this game. Also, the game's missions are all training missions which gets difficult as the player progresses and if certain conditions are met, you can earn new AC parts.
It is difficult to determine whether Nine Breaker is a sequel or spin off of sorts. Two reasons for this are that:1) the Ravens' Ark still exists during this time and 2) no Raven in Nine Breaker appears in Last Raven yet some Ravens from Nexus do appear.
Armored Core: Nine Breaker suggests that the Original Armored Core Universe and the Armored Core 3 Universe are the same. This is because Nine Breaker uses some Nexus Ravens and uses the Universe of Armored Core 3's parts and corporations while also using Nine-Ball who only appeared in the Original Armored Core Universe. Nine Breaker is the 9th game in the series, playing off the Nine-ball reference of the game.
Armored Core: Nine Breaker has been the most widely criticized of all the AC games due to its lack of a storyline, its difficulty, the repetitiveness of its training and arena missions and its lack of any real accomplishment. It has garnered some of the lowest reviews yet out of all previous AC games, averaging less than 5 out of 10 on most official gaming magazine and website review scales.