Uhmm it's just like they said a regas can train a dragon,the dragon is the person who have the bloodline of a dragon.Then just think of a dragon that hasn't been trained properly and the regas is the master or teacher of the dragon to become a better dragon or a better king to maintain the equality of the kingdom.Uhhmm I think that's all sorry if my English is bad
It’s not just you. Although I enjoy reading, even the role of Regas is quite confusing. I just think of it as, if a king isn’t sexually attract to their Regas then it is a brotherhood where the Regas is acting like a second in command giving words of wisdom, but if a king is then…well, the Regas is a side chick. Old record doesn’t say Regas can get pregnant.
It's been a while since the novel and this post will be a mixture of theory and facts as well as spoilers. Read with caution:
The Regas "role" shouldn't even exist in the first place. The Regas is the SYMBOL of the Dragon's affection to the humanity.
The Regas title has been perverted by the council in the span of hundreds of years that the true meaning of being one has been almost forgotten with the passage of time.
I believe there's no true Regas that had been born until Abel, and no true heir to the dragon's might until Karas was born. There's just too many contradictions with how the council presents what a Regas should be:
1. The real Regas was not an advisor to the Dragon.
2. The real Regas was not the Dragon's lover.
But we do know that :
The first Regas planted love in the first Dragon's heart
The last Regas (Abel) planted hate in the last Dragon's (Karas) heart

i reached the 98 chapter..but i dont really understand the job of a regas??how can regas help control anything without powers?? someone explain please