War of the Gargantuas (1966) film directed by Ishirō Honda

Ishirō Honda is a legend in kaju films and for good reason. Even though this film is a sort of hot mess in many ways it isn't without merit. A giant hairy apeman attacks a giant octopus that is attacking a boat and he attacks the boat. It's quite the opening scene. The monsters appears again and again causing destruction and literally eating people and spitting their remains out. It's quite horrific for this type of film at this time. 

Some scientists it seems had a ape kid at some point that ran away and was presumed dead in the mountains and the authorities think it is back, now gigantic on a killing spree. The scientists don't think so as their ape pal was kind and gentle. As it turns out, there are two of them one in the mountains and another from the the sea which... grew from cells of the other but in the ocean so it lived underwater and is sensitive to light? 

The two monsters are at odds, the nice one trying to stop to the mean one ending up in a battle that destroys (surpise!) Tokyo. The two take the fight to the ocean and a volcano suddenly appears from under the surface and maybe kills them both. 

This movie is interesting in that it tries stuff not seen in other giant monster films but it has the feeling it twas made up as they filmed. the "hero" Russ Tamblyn as Dr. Paul Stewart is a smarmy jerk in my opinion and his characters does next to nothing to help the situation. Apparently he was a nightmare to work with and it shows. 

While not a great movie, it does entertain and the model work is really good. The creatures are pretty basic and not the prettiest things you'll ever see.