In BBCS, Noel is manipulated by Terumi into becoming the Sword of the Godslayer, aka Mu 12. In the game, Mu 12's theme is robotic, the lyrics are sung by what sounds like a vocaloid, the melody expresses despair, danger, longing, hatred, all indicative of Noel being overwritten.

But in BBCP, after being brought back by Ragna and with Rachel's help, Noel is able to harness and take control of her Godslayer powers and make them her own, effectively turning Mu 12 into a super form. In BBCP and CF, Mu 12 is not lifeless or evil, she's just Noel.

As such, Mu 12's theme in BBCP onward is given new life. The lyrics are sung with unyielding passion, the melody is hopeful, heroic, confident, powerful, and the overall composition is simplified to match Noel's more organic personality. Hearing them back to back makes me tear up