Jewel BEM Hunter Lime

 is a Japanese PC game released in 1993. It was adapted to a 3-episode OVA released between 1996 and 1997. The OVAs were initially licensed by Media Blasters. It is currently licensed by Sentai Filmworks.
Plot.
Once upon a month, a door behind the full moon opens. This door is between the human world and magical world. Now it just so happens that on one such night, Lime and Bass are in hot pursuit of a demon who had stolen six power gems from the magical world. The demon escapes to the human world through the open door, and the two follow. Now they must search for the six power gems, all of which have been scattered all over Tokyo. It's up to Lime and Bass to blend into with humans and find the gems.