Elsword is Elesis' younger brother. Despite his sister making an appearance at his self-titled game, he has yet to do so at Grand Chase apart from passing mention.
Elsword is the titular and a playable character in Elsword whom was based off of Elesis. Elsword is a young swordman who was raised and trained by his older sister, Elsa (later retconned/re-rewritten to be actually Elesis), the leader of the Red Knights. One day, she left him to lead a mission but never returned, prompting Elsword to set out on a journey to search for her.
In Elsword, the game, Elsa was originally named Elesis. Elesis also being the leader of the Ruby Knights is very similar to Elsa's leadership for the Red Knights. Additionally, there is a concept art on Naver Blog of Elesis and Elsword as siblings; however, due to copyright reasons resulting from the fact that Grand Chase and Elsword are hosted by different companies, this relationship was scrapped.
Elesis was later implemented into Elsword, carrying over her name, personality, red color theme, appearance, and poses, only with their backgrounds slightly differing. Additionally, Elsa had been re-renamed back to Elesis. Likewise, the Naver Blog had introduced Elsword as Elesis' brother in Grand Chase.