The grown-up little Black Dragon wanted to beat up this Guardian Heroic Spirit Divine King.
When the little Black Dragon pulled that child, Iliya, into his domain, he was all set to do just that.
The law-enforcing heroic spirits couldn't enter the little Black Dragon's domain, but he, the Guardian Heroic Spirit Divine King, could easily do so.
What does this tell us?
It tells us that the little Black Dragon was openly plotting with him.
He knew that the little Black Dragon wanted to beat him up.
The little Black Dragon knew that he couldn't hide his intention to beat him up from him.
So, he simply pulled that child, Iliya, into his domain, and the Guardian Heroic Spirit Divine King, driven by his intense curiosity and a desire to witness the little Black Dragon's saga of love and hatred, would definitely be unable to resist his curiosity and would sneak into his domain to spy.
Knowing this, he still entered the little Black Dragon's domain without hesitation.
