The true nature of the core 

Lewis was the son of a devil and a half-giant, half devil.

His devil blood was more dominant but it didn't change the fact that he was the descendant of a giant.

He was also stunned when he discovered he wasn't just the descendant of any giant, but an ancient breed giant.

Investigating the origin of these ancient breed giants, he discovered that they were a breed of giants that reported directly to the origin of all giants;

The Progenitor giant.

This ancestor of his noticed the exceptional talent that let him become a demigod in barely 500 years, and gave him a drop of their blood.

Using this, he performed the ancestral regression spell, and it was a resounding success.

One of the abilities he gained was the giant race's gigantification.

Giants were of varying heights and sizes. Some were as short as 2 meters tall, while some were all tall as 500 meters or even a kilometre.