Ju Ko Kishin Baryon

When countless laser beams come down from the sky and destroy all the countries that hold the advanced weapons, the world descends into chaos. Taiwan, fortunately, escapes the first wave of attack. People then assume that the cities built underwater are immune to the invasion and therefore gather forces under the sea to prepare for the counter-attack. However, they are unaware of the sea monsters that will prove to be the beginning of another nightmare...

(Source: Crunchyroll News)