Complex sentence: A long time ago, the Earth was at the brink of destruction after Demon King Beasts wreaked havoc, but the monsters were sealed with the help of Ultraman and Ultraman Tiga.
Split into simpler sentences: A long time ago, the Earth was in the brink of destruction after Demon King Beasts wreak havoc. These monsters were sealed with the help of Ultraman and Ultraman Tiga.