Tottoko Hamtarou OVA 3: Hamuchanzu to Niji no Kuni no Oujisama - Sekai de Ichiban no Takaramono
Japanese title: ハムちゃんずと虹の国の王子さま 〜せかいでいちばんのたからもの〜
Alternative titles: Hamtaro OVA 3, Tottoko Hamutarou: Hamuchanzu to Niji no Kuni no Oujisama, Hamtaro: Rainbow Rescue
Type: OVA
Source: Unknown
Episodes: 1
Status: Finished Airing
Aired: Mar 24, 2004
Duration: 45 min
Rating: G - All Ages
Studios: TMS Entertainment
Genres: Adventure, Comedy
Demographics: Kids

Based on the third Hamtaro game (fourth in Japan), Prince Bo falls from the sky when the rainbow disappears. Now Hamtaro and the Ham-Hams must help him bring back the rainbow. 

(Source: Wikipedia)