If you loved Gamera: Guardian of the Universe, try Godzilla, Mothra and King Ghidorah: Giant Monsters All-Out Attack
A bridge between a film you've already seen and one most people haven't. Here's what they share, and what the second one does that the first one doesn't.
You already loved

Gamera: Guardian of the Universe
→
Try this next

Godzilla, Mothra and King Ghidorah: Giant Monsters All-Out Attack
What they share
Both films are directed by Shusuke Kaneko, and they both carry the foreign gem mood tag, and they sit in Action / Fantasy / Horror / Science Fiction territory. If that's the register that drew you to Gamera: Guardian of the Universe, the second film will land in a comparable space — through a different lens.
foreign gem
What Godzilla, Mothra and King Ghidorah: Giant Monsters All-Out Attack is
Pacific dusk, sonar bleeps like insect wings. A sub implodes into red mist. Yuri traces painted talons on temple walls to three giants who must wake or watch Japan drown in flames. The kaiju who sleep beneath waves remember every bomb and bullet.