Dai Gattai Don Onitaijin (Japanese: 大合体 ドンオニタイジン) is the central main mecha of Avataro Sentai Donbrothers, the 46th Super Sentai series, broadcast in Japan from 2022 to 2023. It belongs to the five-member Donbrothers team, whose characters are modeled on the Japanese folktale of Momotaro: Don Momotaro (Red), SaruBrother (Blue, monkey), InuBrother (Black, dog), KijiBrother (Pink, pheasant) and OniSister (Yellow, oni/demon). The members transform their avatars into the individual Robotaro machines, which combine into the team's giant robot.

The name "Dai Gattai" (Grand Combination) refers to exactly this merger: Don Momotaro forms the head and torso, SaruBrother the arms, InuBrother and OniSister the legs, and KijiBrother the wings. The head is styled after an oni mask, giving the robot its distinctly demonic and deliberately asymmetrical look that suits the show's unconventional tone. The Robotaro are summoned and powered via the series' signature Avataro/Robotaro Gears (collectible gear discs).

The DX toy, DX Don Onitaijin, is made by Bandai (Bandai Spirits, Japan) and was released in late May 2022. It is built mainly from plastic (ABS/PVC) and is assembled by combining the five individual Robotaro figures. At roughly 35 cm tall, it was billed at launch as the largest DX Super Sentai robot ever, and it offers extensive articulation (including knees, elbows, wrists, ankles and individually poseable fingers for holding weapons). As a store campaign bonus, a limited Robotaro Gear of Don Onitaijin was offered for a time, which triggers voice and sound features on the separately sold DX Don Blaster. The mecha can be expanded with later add-on robots in the line (such as the tiger mecha for the "ToraDora Onitaijin" combination), and a limited Celebration Edition was released as a special variant. Because Avataro Sentai Donbrothers was never adapted into a Power Rangers series, Don Onitaijin exists solely as a Japan-exclusive Bandai product and was never sold as a Power Rangers toy.