just want to clear it up that I have no intention to attack the original story plot lol..I like Saint seiya..i read that manga first and then I am interested enough to read this lost Canvas
Just that I don't think those two mangas are too much related for the following reason
Spoiler for really light spoiler and perhaps a guide for ppl who want to read lost canvas without reading the original manga:
We have 5 heroes in the original manga, but in here, so far we only see pegasus from the original five, and perhaps phoenix from the enemy side and that's it, so you don't need to know the original 5 well in order to read this manga
other thing you may need to know is
1.Hades and Athena play "holy" game/war every 300 or so...their soldiers are willing to die in great number in every 300 years
2.Pegasus, the main hero of this story, can possess god cloth, a cloth that outshines even gold cloth..and the reason that Pegasus has god cloth seems to be related with the fact that Pegasus has always been the one to hurt Hades badly in every 300 years...so he has deep bonds with Hades and Athena
3.Soldiers from both sides, as well as Hades and Athena, can be reincarnated in every 300 years in order to start this "holy" war, but they don't have the memory of the past...even for Hades and Athena (I am not sure whether this applies to Hades and Athena, but it seems like it)
And the info in above is all you need to enjoy this manga..you don't really need to read the original manga lol..even if you don't read the info in the above, in my opinion you still won't get lost, except maybe for chapter 77, and ppl in above have already kindly explained it XD