Cerberus

Summary
Cerberus is an animal-like monster that strongly resembles a dog from Naofumi's world. The monster is pitch black in color, and wields three individual heads with enormous fangs.

The Cerberus appear out of the several rifts in the sky during the First Wave and attacked Raphtalia's village. The Cerberus was the Wave Boss of the First Wave and was never defeated. Along with other monsters, Cerberus completely destroyed Raphtalia's village and killed most of the resident villagers, namely Raphtalia's parents.

The whereabouts of the Cerberus are unknown after the events of the First Wave, and it's unknown whether it is still alive or already deceased.

Debut

 * Anime: Season 1, Episode 2
 * Manga: Volume 1, Chapter 4
 * Light Novel: Volume 1, Chapter 16 (mentioned) &amp; Volume 1, Special Extra Chapter Two (actual)
 * Web Novel: Chapter 19

Trivia

 * The Cerberus killed Raphtalia's parents in front of her eyes, causing her to develop a trauma of blood and dog-like monsters.