MAZINGER OTOME TAISEN

After another day of school Seto Magami is walking home with Reito and Koji. However they meet two young women named Necro and Bui Jinga, earlier Mazinger android models who were also created by Juzo Magami and they pick a fight with Seto and Reito, ultimately overpowering them. They leave saying they won't be as merciful as they were. Meanwhile Grace and Shiko encounter their own doppelgangers in the form of Dark G. Dark and Shin Kotetsu who explain their intentions rather than fight. Necro recruits them to form the New Mazinger Army before getting into another brawl with the Mazinger Army. During the battle, Shiko and Shin accidentally fuse together to become Majeeg which became a problem for both sides so they decided to work together. But Majeeg proved to be too powerful for even their combined forces until Seto entered her Astro Mazinger form and after overpowering Majeeg purged the evil from it, freeing Shiko and Shin. Afterwards, both the Mazinger and New Mazinger live on (relatively) good terms. — Description from AniList community (anilist.co).