A/N: This is completely based off my head-canon that Sirius is a Scorpio and the irony that comes with it. I don't own HP nor do I own the Legend of Orion.
"I wonder when the boys' birthdays are. Maybe I could buy them small gifts or something." Lily Evans mused, turning a page in the crime novel she was reading in the Gryffindor common room.
"Hey, Lily-flower." James said, flopping onto the long sofa opposite her, as three of the other Gryffindor boys did the same.
"Evening, Marauders. When are your birthdays?" She answered, closing her book and leaning forward to rest her arms on her knees. The four boys looked at her oddly. She huffed and repeated herself. "When are your birthdays?"
"We heard you, darlin', we're just trying to figure out why you want to know." Sirius answered.
"Because I don't know. Why else would I ask?" She asked, shaking her head.
"Mine is March twenty-seventh." James answered, digging out a practice Snitch from his pocket. Remus revealed that his birthday was September seventeenth, while Peter's was on February twenty-third. Lily looked expectantly at Sirius.
"November tenth." He answered. Lily paused for a moment, then snorted, which slowly evolved into full-blown laughter. "What?" Sirius asked, puzzled.
"You're a Scorpio. Your name is Sirius Orion." She answered, hysterically. Remus looked at her and started laughing with her. The other three members of the Marauders looked at them oddly.
Peter then slowly spoke up. "I don't get it."
"Don't worry, Pete, you're actually not the only one." James answered, regarding the werewolf and muggle-born with a wary expression.
Lily calmed down enough to give them an explanation. "Orion was one of the greatest hunters that ancient Greece had. He was the son of the god of the sea Poseidon, and Eurayle, the daughter of Minos, the King of Crete. Being a son of Poseidon, he could walk on the water. He traveled in this way to the island of Chios, where he got drunk and assaulted Princess Merope, daughter of King Oenopion. Oenopion blinded Orion, who stumbled his way to Hephaesto's forge in Lemnos."
"Who's forge, where?" Peter asked, lost.
"Hephaesto. The god of metalworking and blacksmithing. He was lame in one leg due to a birth defect." Remus said, conjuring a map of Ancient Greece. "That's Lemnos. This one over here is Crete, and this one is Chios." He said, pointing out the three islands.
Lily continued "Hephaesto made his servant Cedalion take Orion to Helios, the god of the Sun, who healed Orion. Orios returned to Chios to exact revenge, but King Oenopion hid in an underground chamber where Orion couldn't find him. Giving up, Orion then made his way back to Crete, where he participated in many hunts with the goddess Artemis, her mother Leto, and Artemis' band of followers. He got so into their last hunt that he threatened to kill every animal in the world."
The Marauders, minus Remus, gasped. "What happened then?" James demanded.
Lily smiled and continued "Gaea, Mother Earth, objected and sent a giant scorpion to kill Orion. The scorpion succeeded, but Orion gave it such a fight that they both died from their wounds. Orion's dog Sirius was killed, attempting to defend his master. Artemis begged her father Zeus to place Orion in the heavens. Gaea placed her scorpion in the sky as well, though on the opposite side from Orion and Sirius, so that they are constantly chasing each other, trying to continue their fight."
"So the fact that I'm is a Scorpio is funny?" Sirius asked.
"You don't get the irony, do you? Your name is Sirius Orion and you were born unto the astrological house of your namesake's greatest enemy." Remus answered, still laughing. The other three Marauders shook their heads in confusion, and started a three way battle of Exploding Snap, while Lily and Remus chuckled to themselves.
"You want to know another piece of irony?" Remus asked. Lily nodded once. "I was born on a full moon." They shared a laugh as Peter's eyebrows got singed off.