The artist of the manga this series is based on, known as SankakuHead, makes several appearances throughout the anime, including in the opening, where in a Mario-Kart style segment, Umaru throws a hamster at the go-kart in front which contains SankakuHead, and at another point where Taihei (Onii-Chan) is in a car and keeps having to break before he sees the author and exclaims, "AAH! A mangaka!"
The sections of the opening are all inspired by popular games - first classic Pokémon games, then Mario Kart, then Monster Hunter, and finally Disney's TsumTsum range of mobile games.