As the four children hatched from the two eggs their mother had miraculously laid, they started crying from entering the world. Being dubbed Hikaru and Kaoru, in the respective order they were born, they looked the same and even seemed to cry at the same time and way.
Even though they were identical, they had one difference, causing them to be a world different. They were born from different fathers, Hikaru being born from Ranka, the King of Sparta, and Kotoko, and Kaoru from Kotoko and the chief god Zeus.
From another egg, two girls were born, Haruhi and Kasandora. Kotoko held the two sets of twins in her arms and wondered about the simple things in life.
Being the king's sons, it was only natural that they were well-educated, strong-willed, and very daring. They were known by all of the ladies and Hikaru and Kaoru would often play games with them. However, they would never get very far, to the ladies' disappointment because they would often lose interest before they went too far.
They loved their sisters very much and were very protective of them. Haruhi and Kasandora were both very beautiful, Hikaru and Kaoru were always tough on anyone who dared tried to seduce either one of them, since they knew that besides Ranka, they had the final decision on who their sisters would marry.
In Sparta, they were healers, physicians, and protectors, only adding to the ladies' affections. Among the years, they were all of these things.
The famous Tamaki came to recruit them one day, to join him and were joined with the Argonauts along with Kyoya, Mori, and Mitsukuni, or 'Honey'. Together they accommodated ladies everywhere. Tamaki was the 'prince' type, which was ironic, since he is prince of Mycenaean Sparta*. Hikaru and Kaoru had heard about him since he was so close to where they lived. Tamaki was a close friend of the twins but they would often mess with him*.
Kyoya was known as the 'cool' type. He was often nonchalant about everything causing the ladies to go crazy over him and could play the lyre^, which was a distinguished talent. They never really understood Kyoya, he was always managing the Argonauts* making sure they don't go bankrupt*, but they realized he was cool and didn't mind him badly.
Mori was actually closely related to the twins (Kaoru), since his father was also Zeus. Honey was kin to Mori* and Mori treated Honey in a way that Hikaru and Kaoru understood, like brothers*. Mori and Honey were very nice to Hikaru and Kaoru, making them feel like family, which they were*^.
Besides wooing ladies for money, the Argonauts had another goal, to obtain the Golden Fleece, so that Tamaki could become king.
Along their journeys, they passed the isle of Lemnos, where all of the Argonauts^, except for Mori, had been seduced by the women of Lemnos, who were without men since they had killed all of them when the men had avoided them for the stench Aphrodite had put on them. Well, the twins were ALMOST seduced*, but they were talked out of it by Mori. The three of them had finally convinced the others to leave, but Tamaki had already impregnated the queen with twins^.
At the end of their adventure, they obtained the Golden Fleece. On the way home, they passed by Sirenum scopuli. An island rumored to have sirens. Beautiful music was heard and they started to go towards the islands, if they would continue on this way, it would eventually crash them. Kyoya pulled out his lyre and started playing louder and better than the Sirens' songs and the crew came to and maneuvered the ship out of harm's way.
Word had been sent to them that Kasandora had been married. They rejoiced with the other Argonauts, but were later disrupted by more word from home that Haruhi was captured by the Trojans.
The twins got the rest of the Argonauts to go rescue her* when they had succeeded and the rest of the Argonauts had seen her, they fell in love with her*. Hikaru and Kaoru could understand why they too had been infatuated with their sister for a time* but had eventually talked themselves out of loving her since it would be best for her.
The Argonauts soon disbanded after Tamaki became king* and Hikaru and Kaoru went of on their own adventures, but before they did, Haruhi was at the age of marriage and it was needed for them to be there to make the decision, along with their father, who would marry her. The suitors brought luxurious gifts but the twins disliked most of the suitors themselves. Finally, it was decided that straws would be drawn to who would marry Haruhi (Ranka's idea, with the twins' great disapproval). Tamaki ended winning the hand of Haruhi for marriage.
The twins went off and had fallen in love with the betrothed daughters of Leudippus. The daughters were betrothed to their cousins Idas and Lynceus of Poseidon, by rumor. Hikaru and Kaoru challenged them for the daughters' love and had defeated them, but not without Hikaru being mortally wounded by Idas.
After Hikaru passed away, Kaoru tried to commit suicide to join his brother but couldn't since he was immortal. Kaoru begged his father to give half of his immortality to Hikaru, which he did.
However, they were doomed to a split life. They must live one day in Olympus with the immortals and another with Hades.
It is said that you can see them in the sky, together, forever.