It's Gamera on Gameboy and the title translates to "Guardian of the Universe" to coincide with the movie of the same title. This is a fighting game of sorts. The whole game you play as Gamera and you fight one monster after another interspersed with dialogue and scenes.
All the fighting is turn-based and you execute all your attacks with button combos. The combos are pretty simple it's usually something like hold left and press B and there are many defensive and offensive maneuvers to perform. It's even pretty helpful by providing an in game move list that lists every combo.
Also the game is entirely in Japanese, but there are fan made translations that can be found online.
The game provides the platyer with great music, great graphics, and great sound effects and even the controls while hard to adjust to aren't that difficult and are presented on screen for you. The game-play is like if you took Pokemon removed the trainer from the equation, had it just be battles, made some better animations, attacks and transitions.
It's pretty monotonous unfortunately. You fight monsters, from every Gamera movie, in front of indistinct backgrounds and then the game culminates when you beat the last one, you end up fighting a Gamera clone.