Iselus

Icelus El-Arde Corwen is Rayneshia's younger brother and is the primary candidate to succeed Duke Serjiad Corwen, although his father Feynail currently serves as his guardian.

He was first introduced in the Log Horizon TRPG supplementary material, but made an official appearance in volume 10's material.

Prior to the Catastrophe
Like his sisters Risselthea and Rayneshia, Icelus is the child of Feynail and Sarariya, and thus the grandson of Duke Serjiad Corwen. Because Serjiad himself has no sons, Icelus will inherit his place in the League of Freedom Cities Eastal, despite being a little less than eight years younger than Rayneshia and much younger than Risselthea (who married a knight and thus denied from inheritance).

Return of the Goblin King arc
Although Icelus is not officially seen in this arc, he was aware of the Adventurers' help in defeating the main Goblin forces and began idolizing them after that.