As a result of the distorted time-space of the Annex World, inter-dimensional portals of different worlds open and begin to intertwine with one another…Cortex Commander and his army of cybernetic cerebral soldiers have traveled through one of these inter-dimensional portals to continue their diabolical campaign. Known as The Ruthless Mastermind of Chaos, Cortex Commander and his army have only one thing on their minds: intergalactic domination. Cortex Commander is linked with his medulla marines through a complex neural network, allowing him to control his legion of Cortex Infantry and Cortex Flame Troopers with surgical precision. Using mechanized suits and repurposed weaponry from defeated enemies, the Cortex Army continues to grow. Enemy combatants and anything foolish enough to get in the way are gone in an instant, like synapses firing in the brain – mind obliterating matter…With the entire world in peril, will anything be able to defeat Cortex Commander and his bloodthirsty brain brigade?There are good guys. There are bad guys. Then there are… The Worst x Acid Rain World.

Annex 的時空發生扭曲，不同世界的次元入口因此敞開，並產生一連串連鎖效應…科泰斯將軍及其率領的大腦軍團穿越其中一個次元，並持續擴張他們的邪惡勢力。科泰斯將軍有著「渾沌暴君」的稱號，他的軍隊只有一個目的─那就是統治廣大的星際空間。科泰斯將軍使用一種複雜精密的神經網路系統與他的髓質陸戰隊部下建立聯繫，能夠以外科手術般的精確度控制科泰斯步兵以及科泰斯火焰兵軍團。科泰斯的大軍會將其手下敗將的機械化武器裝備納為己用，因此勢力越來越大。對手的戰鬥人員和任何螳臂擋車的事物都會被瞬間消滅，如同大腦中的突觸般被逐一清除…全世界正陷於危機之中，到底誰能擊敗科泰斯將軍和他的嗜血大腦軍呢？ 世上善惡明暗並存，更有著…The Worst x Acid Rain World.