Kidou Senshi SD Gundam no Gyakushuu
English title: Mobile Suit SD Gundam's Counterattack
Japanese title: 機動戦士ＳＤガンダムの逆襲
Type: OVA
Episodes: 2
Source: Original
Genres: Comedy
Studios: Sunrise
Duration: 12 min per ep
Rating: PG-13 - Teens 13 or older

It consists of two parts:

1. "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.

2. "The Tale of the SD Warring States: The Chapter of the Violent Final Sky Castle" - Set in the fictional land of Ark, SD Sengokuden re-imagines the mobile suits and mobile armors of the existing and more serious Gundam stories as super deformed sentient samurai in a setting reminiscent of ancient Japan.

(Source: Gundam Wiki)