Hi,

Some years ago, I saw a japanese music video on youtube. The song was part of a big compilation. Each song was a chapter of a story. What I remember is that it depicted the life of a brother and sister with a royal lineage. They were twins and had to fight each other at some point. They were blond and had blue eyes. In one song, there was a line about swan singing when they die. These songs were made by a known artist in the video game world.

Does anyone knows what it is called? I've been searching for days but I can't find it T_T

Kinda shooting in the dark since I haven't seen such music video, but maybe Okoborehime to Entaku no Kishi? Seemed the closest to what you described. The closest tag I could find fitting the description of brother and sister conflict is 'Sibling Rivalry', and combining that with one of the royalty tags it brought a couple results.

If it isn't this title, you might want to run a couple queries using the aforementioned tags and checking the results, it's not that many. Or hopefully someone who knows the answer will be able to post at some point.

I'm guessing it's most likely from the Story of Evil series by Akuno-P.

"Aku no Musume" and "Aku no Meshitsukai" might be the one you saw. But there are others in the series. And I cant recall any swans or killing each other. He traded places with her to die in her steed actually.