Where does “ケルベルス” come from?

ケルベルス (Japanese) comes from Latin Cerberus, from Ancient Greek Κέρβερος — Cerberus.

ケルベルス (Japanese): Cerberus

Definitions

Step	Language	Word	Meaning
1	Latin	Cerberus	—
2	Ancient Greek	Κέρβερος	Cerberus

ケルベルス — Etymology, Origin & Word History | Etymology Explorer