Kidou Senshi SD Gundam no Gyakushuu

There are 2 parts to this...
In "The Storm-Calling School Festival", Char and Haman host a festival to celebrate the union between the Nu School for Boys and the Zeta School for Girls. But all hell breaks loose when the Counterattack School gang - led by Amuro, Judau and Kamille - rush in to crash the party.
'The Tale of the SD Warring States: The Chapter of the Violent Final Sky Castle' is the second part of SD Gundam's Counterattack.