Esseba looks like a 68 years old man, and is described by Rou as a good-looking uncle.
Esseba is the 3rd and current head of the Failuo, the originators of the Rheinfall clan, which are primarily in charge of fighting.
Prior to Rou's birth, he ranked up into a High Elf after 100 years of training. He's currently 340 years old.
It's presumed that the Elite Elves under the supervision of Rou were attached to his clan, but he didn't pursue it after thinking about the risks of antagonizing Rou. To prevent unnecessary sacrifices and fighting, he kept it secret with a cover-up.
Mail Failo Rheinfall (Daughter)