Ore-sama Quest was released June 23, 2006. It was released to run on windows XP and later had a patch released to allow it to run on Vista.
Just like in the anime, Yuuri Shibuya got flushed down the toilet out of his normal, average life into an unknown world, thus being appointed as the new Maou (Demon King). The game has three "events" -- the festival, the dance/party and something concerning Gwendal.
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