Mr. Osomatsu is based off of the gag manga series Osomatsu-kun by Fujio Akatsuka, and ran from 1962 to 1969.
The Mr. Osomatsu OAV, which is titled Mr. Osomatsu: ~Hipipozoku to Kagayaku Kajitsu~ (“Mr. Osomatsu ~The Hipipo Tribe and the Glimmering Fruit~”), starts its theatrical release on July 8.
The series features a set of sextuplets, the Matsuno brothers, with Osomatsu being the oldest brother and leader of the group.