Every Saint was killed less than thirty years ago
If you read supplemental materials, or even just go looking at the characters themselves, you'll realize they're all in their late teens and (at most) early twenties. These are saints, some of the most physically fit and cosmically in-tune people on Earth; each bronze saint should be living to their late eighties without need of seeing a doctor, and doubtless there's ways they can use cosmos to heal most injuries and illnesses. So why, then, are they all so young? My guess is they either fought a god or a deity figure some time before Athena was reincarnated to lead them, and thus an entire generation of them died defending the Earth. More sinister options include that they are systematically killed when they get too old! Libra Dohko and Aries Shion, the oldest living saints at 260 years old, may have enforced an age limit to avoid a rebellion or perhaps to keep them young and powerful. (Yeah, I know it's a stupid thing to do considering it would entail having a good number of years being defenseless, but this isn't Sensible Mass Guessing, is it? ^_~)
- A normal bronze saint may be physically fit, but considering the arduous route to get in this condition, most of the candidates actually die before they can even hope to get a cloth, (remember, of 100 kids they sent into training only 10 survived) isn't that surprising. Also having a body incredibly healthy doesn't mean you will live to see your eighties, if you consider the violent environment they live, Internal fights (which seem to happen a lot on the rule of Saga as the pope) and minor crisis tend to take high tolls of the saints in turn. Also they probably wouldn't be as much as a hurry to recruit people until Athena is reborn or the next Holy war get near which is 200 hundred years each time. It is probably easier to manage fewer but more effective saints between conflicts.
Phoenix Ikki knew, deep in his soul, that Andromeda Shun was Hades (or at least something that could destroy the world) reincarnated.
Shun was probably the one who killed their mother, even if it was an accident, so, Ikki tried to make him avoid fully intentional bloody situations ever again; not really because he was worried about his brother, but because he was worried about the entire world. It explains why he was so eager to exchange armors with Shun; he knew that if his brother ever got the Phoenix armor, the world would be screwed.
- Pretty much confirmed in Lost Canvas (though I heard the creator is kinda iffy on how strong it is as canon). Ikki is the reincarnation of Bennu Kagaho, who protected Alone/Hades for similar reasons (runaway little brother). He vows to follow Alone's reincarnation and protect him rather than Hades.
Seiya is Haruhi.
C'mon, this theory should be here someday. Also, it'd make lots of sense on how a "mere mortal" can defeat gods. Also, losing all his five senses, but still fighting? Please!
Sailor Moon is in the same universe as Saint Seiya.
With Saints and Sailor Senshi being distaff counterparts of each other, natch.
And Wonder Woman
Mitsumasa Kido was Zeus
- This is pretty strong Fanon in the Latin American communities. It would make his appearances to Saori make more sense. Since otherwise, there is no justification to them, being a mere mortal, sex drive notwithstanding.
- Actually, I'm pretty sure that the "appearances" were just holograms generated by Planetarium. Didn't the appearances stopped after the Planetarium destruction?
Cepheus Albiore is June's father
She's doesn't train with the other Amazons. She's from Ethiopia, but doesn't look like it. The two share a lot of the same traits (blond hair and dark blue eyes). In the show, Esmeralda is Guilty's daughter so is it too far fetched that the two are related as well?
Balrog Lune is June's brother
Two hot long haired blonds with a liking for whips and similar sounding names? What are the chances!
The Steel Saints didn't just take the wrong plane...
- rumor has it that they washed up on a deserted island, resorted to cannibalism with Daichi being the first on the platter.
Aioros trained Marin.
Because it makes for a nice Master Apprentice Chain.
Seiya and everyone else (including those in spinoff titles like Saint Seiya Omega) are older than you think.
They claim to be 13-18 years old. However, I seriously doubt that was the case. They can be physically in their twenties. Excepting that in Saint Seiya-verse, age counting is handled differently. It could be that one person's age in that verse increases after MORE than 365 days (standard age increasing measurement). Therefore, Seiya and the rest could be around the twenties by default, but by the measurements of the SS-verse, they're just 13-18 years old.