Satou

Has known Hime since she came to Earth 10 years ago with Gramps.

He forces his way into the portal to Hime's world ash she and Gramps are returning to their world to fight the Abyss. He ends up "married" to her and obtains the Ring of Light, becoming the new Ring King.

He then travels with a number of people on and off, but mostly Hime and Gramps. As he marries the other Ring Princesses, they join him in his travels and gains their rings as well.

Relationships
Hime is always number one in his eyes. It takes a steel will to resist the more aggressive advances of the other princesses. They have tried to "do the deed" a number of times but always end up being interrupted by someone.

Nephrites has a curiosity towards him and is fine being second behind Hime as long as she gets her turn. She later becomes more aggressive towards him. She can no longer deny her strong feelings and isn't okay with just waiting for Satou to love her.

Granart is unimpressed by him at first. As she sees how capable he is while traveling with him her lust towards him to make strong babies turns into love. She becomes shy when he touches her and has a desire to be loved back after he awakens her fire magic.

Saphir isn't interested romantically towards him as far as it is shown in the story. She does get mad when he won't pay attention to her advances even if they are made in jest or to do her duty to make a strong heir for her country.

Amber was created to be with the Ring King by the now gone Dwarves. She is fine devoting her everything to Satou and is willing to protect him even if she would die. Whether these are her own feelings or how she was programmed remains to be seen.