Definition: To equip, To clad
Like Henshin, this phrase is often shouted by transforming heroes when they transform.
While Henshin means that the body is changing, chakusou means "To put something on" or "To clad" like putting on armor.
The series Tomica Hero Rescue Force and Tomica Hero Rescue Fire both have heroes who shout Chakusou when they transform. The heroes in these series are all human, so they are essentially just putting on powered suits. The phrase was also used in another tokusatsu series Kyuukyuu Sentai GoGo V, which aired nearly a decade before the Tomica Hero Series.