Supposedly the game talks about Elsword's "sister" who was a "great general and warrior" who went on some sort of "long journey". Now to me, sounds like boring old cliche backstory, but a lot of the newbs go "lulz, iz Elasus brather!". So whatever. They've said before that ElSword is in no way related to GC, it's just the same style of gameplay, and they kept the color schemes and classes. Different world, different people, different story.
The relationship between elsword and elesis is simple
both games were made by the same company, therefore they are obviously blood related. Hurrrrr stupid nubs don't know anything about game development. It's obvious they are related because the color schemes match the original characters. and the gameplay is almost identical! Thats why Elsword is Elesis's brother, otherwise you're an idiot for questioning this undeniable logic!
And Rena's hotness is much higher than Lire and Amy combined.