This is a show called attack on titan, it is a Horror/Action show. Attack on titan is about a character named Eren Yeager who joined a force to reclaim land that was taken from them by the titan due to the introduction of new variants of titans called the "Armorred" and "Collasal" But during one of the missons Eren was eaten by a titan which had awakened his ablity to titan shift. Years later eren caused the mass genocide event called the Rumbleing