Amazingly hilarious 1986 Toaplan game about visiting various planets and then assaulting the local wildlife. This includes blue ewoks, and rhinoceroses. It's quite short; a 1CC's about 9 minutes long, and difficulty scales massively in the loop as everything does double damage. I only get a few levels into the second loop.
Super Punch is devastatingly powerful, and hilarious to melt bosses with.
Quite an easy game too aside from the last stage, it took me about an hour and a half of play to figure it out and get the 1CC. The last stage is the major hurdle, and I still made rather a mess of it!
The American release, simply named "Guardian", is far harder. You have half the health on the default setting (making it roughly equivalent to loop 2 here) and a few bosses are made tougher, particularly the first boss.