Bangai-O is a multidirectional shooter developed by Treasure and released in 1999 on the Nintendo 64 in Japan. It was ported to the Dreamcast worldwide shortly after with some gameplay changes and updated graphics and audio. The game places the player in control of a weaponized mech that can hover across large stages and fire at enemies all around them. The player must reach the end of each stage and defeat the boss, while avoiding hazards scattered across the map such as enemy mechs and gun turrets.

Treasure Co., Ltd. is a Japanese video game developer based in Tokyo known for its action, platform, and shoot 'em up games. The company was founded in 1992 by former Konami employees seeking to explore original game concepts and free themselves from Konami's reliance on sequels. Their first game, Gunstar Heroes (1993) on the Sega Genesis, was a critical success and established a creative and action-oriented design style that would continue to characterize their output. Treasure's philosophy in game development has always been to make games they enjoy, not necessarily those that have the greatest commercial viability.