Some of the characters get together and talk about "regrets" they have after 4 years of anime Gintama. Soon they fight over who gets more screen time. Special animation shown at the Gintama Haru Matsuri 2010 live event.
9Anime is the best site to watch Gintama: Dai Hanseikai SUB online, or you can even watch Gintama: Dai Hanseikai DUB in HD quality. You can also find Sunrise anime on 9Anime website.