With the declaration of war against the Dark Army, Psycho was brainwashed and Noomaru became Onmitsu, leaving Musha, Mark Two, Zeta, Double Zeta, and Nu to fight against the Dark Army as the "Five Mushas". Even though two of them have left, their reputation as the strongest remains unshakable.
Psycho had freed from brainwashing and Noomaru completed his role as a spy, joined them, and the seven were reunited. The seven gundams, known to the world as invincible, were given the title of "Musha" and formed this strongest team, and all of them have sworn to be blood brothers as the children of Sho Gundam.
In the World Unification arc, they were seen in their younger days as the Young Musha Team (incidentally, only Musha Gundam looks the same as it does now).
They were inspired by the protagonist machines of the Gundam series, with the exception of the Psycho Gundam.