Box Weapon Prototype is the 146th episode of the Katekyo Hitman Reborn! anime.
Tsuna, Yamamoto, and Ryohei are called out to Namimori Middle School, where they encounter Mammon, who reveals he has Kyoko hostage. Mammon begins Tsuna's trial with a set of riddles which leads them to various locations. The final riddle leads them to Namimori Shrine, where he reveals he does not actually have Kyoko hostage. Mammon uses a Box Weapon and releases a starfish to battle the three, but is quickly defeated. Tsuna passes Mammon's trial of adaptability and receives the seal. Reborn asks Mammon about his Box Weapons; the latter replies that the boxes have been showing up in the mafia and that the Lightning Arcobaleno Verde has asked him to test them out.