Published inside the 3 Anime Speicals[アニメ スペシャル], each have an outside story[番外編 ストーリー: Bangaihen Suto-ri] that complements the TV series. One of them don't really fit in the TV timeline but two of them explains some unclear events in the show. The stories were written by the show writers.
[You can read the translation of all 3 Outside Stories here ]
Nebula Chain, Bond of Brothers[星雲鎖 兄弟の絆: Seiun Kusari Kyoudai no Kizuna: Star Cloud Chain Bonds of Brothers]
This story was printed in Anime Special 1 which was published on July 13th, 1988. It was written by Takao Koyama and have illustrations by Nobuyoshi Sasakado. It doesn't fit in the series timeline but it happens after Ikki is buried by Docrates. The story centers on Shun who is wondering where his brother is. He has nowhere to stay so Saori allows him to stay in Kido Mansion. That night Dark Saints comes and attack him but they are not just any Dark Saints. They have been trained by Pope Ares and have a power like Gold Saints. Ikki finally appears to save Shun and reveals they were the Dark Saints he knew on Death Queen Island. Ikki defeats them and retrieves back a memento from Shun and Ikki's mother.(1)
Saga! Prelude of Desire[サガ！ 野望の序曲: Saga! Yabou no Jyokyoku]
This story was printed in Anime Special 2 which was published on Nov. 9th, 1988. It was written by Takao Koyama and have illustrations by Shingo Araki and Michi Himeno. This story is a prequel story. 1 year before Athena descends to Athena Temple, Shura returns and meets his old friend, Aiolos. That night, the Pope is attacked by an assassin wearing Scale[鱗衣]! It is during this battle that Shura's arm finally gives birth to the skill, Excalibur[聖剣: Seiken: Sacred Sword]. He uses the skill to fend the assassin off. Later that night, the Pope's little brother, the Silver Saint Ares(2), notices that Saga has the wounds made by Excailbur. Saga kills him for knowing, and from then on, he pretends to be Ares waiting for the right time to kill the Pope and Athena. The story ends with the scene of Shura hunting Aiolos.
Athena! Her Great Love[女神！ 大いなる愛: Megami! Ooinaru Ai: Goddess! Great Love]
story was printed in Anime Special 3 which was published on Apr. 19th,
1989. The story was written by Yoshiyuki Suga and have illustrations by
Shingo Araki and Michi Himeno. This is an inquel story between Sanctuary
Chapter and Asgard Chapter. Sanctuary is celebrating the Advent of Athena,
however, Athena is very worried about Seiya and starts to have feelings
for him. Mysterious warriors comes to attack the Bronze
boys while they are still recovering at Athena's Spring. Ikki and Shaka
fends them off. The story ends with the scene of Syd fighting with Seiya
and Athena finally understands what it means to love as Athena.
Supervised by Masami and written by Tatsuya Hamazaki are 2 novels detailing the present era fight between the Gigas Giants and the Saints. Tatsuya used the sources the Great Holy War History and Encyclopedia to write his story. Tatsuya says his novels are not a parallel world story but another interpretation of the Saint Seiya world. The first novel was published in Aug. 28th, 2002 and the second novel was published in Dec. 21st, 2002.
Gigantomachia Mei Chapter[ギガントマキア 盟の章: Gigantomakia Mei no Shou]
The story begins with Silver Saint, Altar Nicole and Shun goes to see a
play, "Oresteia" at the Acropolis in Athens. While the play was still in
the second act, "Choephori", a mysterious man comes and kills the actors
on stage and tries to attack Shun and Nicole. The man then with Gigas Giants
wearing armors called, Adamas[金剛衣: Kongou I: Indestructable Cloth] goes
to Sanctuary and abducts Bronze Saint, Sextants Yurij, and takes her to
Nicole orders Mei who was one of the 100 orphans to guide Seiya and Shun to Sicily. After fighting with the Gigas Giants, joined by Hyoga, they enter under Mt Etna to the Underground Temple of the Gigas. Because of the binding field[結界: kekai] of Pregra[地炎: Chien: Earth Flame], the Cosmo and blood are sucked to help the resurrection of the Gigas God, Typhon!! The chapter ends with the revealation that Mei is to be the Coma(Hair Constellation) Saint!!
Gigantomachia Blood Chapter[ギガントマキア 血の章: Gigantomakia Chi no Shou]
Mei is revealed to be the true heir of Mitsumasa Kido and step-big brother
to Saori. 6 years ago he was willing to be sent to Sicily and trained under
Death Mask!! DM sent him to the Underground Temple and Mei was brain-washed
by Typhon's Will and unsealed the Gigas Giants.
In the present time, the other Saints are sent around the world to find the Gigas. Typhon resurrects new Gigas Giants and uses Echidna to birth him a new body. Shun finds the Giants at Anatolia(Turkey) and gets beaten by them. The Giant Pallas kills Yurij at Sanctuary and confronted by Mei and Shiryu, he kills himself. Torn by the guilt of her death, Mei goes alone to Anatolia. Seiya, Shiryu, Hyoga and Nicole follows after finding this out. Nicole is killed and the 3 Bronze fights the new Gigas Giants. Ikki appears and destroys the new Typhon body. The story ends with Mei sealing Typhon by the help of the stars and his own Coma Cloth.
Further Reading and Reference Sources
Here's a list of sources for fans to read up on Saint Seiya knowledge:
Notes and Trivia
1. Although the memento is a cross in the
story, this idea a precursor to the star pendant of Hades Chapter.
2. The story don't reveal what constellation Ares has but in Saint Seiya Encyclopedia, it reveals that there is a Silver Altar Saint that can act as a decoy to the Pope.