Sangeki no Kioku (S01E07)

Menel leads Will to a village that's being attacked by monsters. As he banishes them, he learns gravity of the tragedies caused by the attack. Piled-up bodies and burnt houses are everywhere. Then, from their midst, a faint voice catches Menel's attention. The voice belongs to a severely burnt young boy who has turned undead. (Crunchyroll)