Developer: University of Tokyo
Based on: A damn weird fusion of academia and Japanese history.
Heiankyo Alien is an arcade title originally developed by the University of Tokyo's Theoretical Science Group in 1979. You play the role of a kebiishi with the task of holding back an alien invasion in ancient Japan. Your only weapon is a shovel, and your goal is to lure enemies into the holes you dig, and then bury them alive. Imagine something like Lode Runner? played from a top-down perspective. The arcade version was cloned and copied (Sega released a version called Digger in the U.S.), and the rights had been passed around like a hot potato before being revived as a Game Boy title in 1990.
This version includes a port of the arcade game as well as a remake that updates the original's stark levels with a period-inspired facelift and adding new play elements like moving walls and undiggable floor panels. The sprites and animations are very expressive, especially the kebiishi's many gruesome deaths.
That it only has 12 stages seems criminal, but I've never made it past stage 8. Advancing is sometimes a matter of luck because of the alien's erratic movements. You can play it safe by surrounding yourself with holes, but if the aliens come in pairs you might be screwed, since they can help each other out of holes. Yet this very same brutal level of difficulty keeps me coming back to it time and again -- a simple arcade challenge that anyone can dig.