The staff of 'Protect the Earth' revealed, "Key, who had been active as a musical actor in works such as 'In the Heights', 'Zorro', and 'The Three Musketeers', will be playing the role of Byung Goo in the play and act along with the #1 ranked actors in plays."
The play is based off a movie of the same name, and is an SF genre. Key's Byung Goo is actually an alien, and he'll be going up against Kang Man Sik, an Earthling who had hurt Byung Goo.
It'll be Key's debut into theater, and he'll be a rare idol that's active in a non-musical play. Curtains will go up on April 9th.