DENKI SOUKOU RAIJIN

Denki Soukou Raijin summary:

A young man called Kanou Ryoto was once saved as a child by a mysterious hero named "Raijin".
Ten years later, Ryoto works in his sister's dog cafe. While walking the dogs one day, he happens to save a strange dog from drowning. Soon after a monster attacks his sister and suddenly the dog he had saved earlier starts to talk to him. Not only that, he also teaches him how to transform into a battle hero and protect his loved ones.
This is the fateful moment Ryoto changes into Raijin Model One!