This is another slightly complicated answer and I’ll first need to provide some background on aspects of this verse I don’t talk about on here as much. (I’m going to discuss omegaverse-related subjects so this is just an fyi for that.)

As noted on my sidebar about and FAQ, L&L-verse is what I call omegaverse!lite. There’s some lore behind why this is the way things are in-universe, but for the purposes of this ask the important things to consider are that, like omegas in omegaverse, people experience heat cycles that happen every 3 months or so (aka about 4 times a year). This is something most people experience, is part of daily life, and as a result it’s fairly common for friends-with-benefits relationships to form, especially among single people, for the purpose of helping each other out with heats without the worry of romantic relationship/pair bonding commitment or partaking in one-night-stands (one-heat-stands?) with people you don’t know as well or even strangers.

This type of relationship was sort of what Cyrus and Saturn had, though on the more “professional” end of things. It was definitely not common for this fwb type of relationship to happen between boss/second in command but neither of them are conventional people so it was what it was. Saturn initiated things, having feelings for Cyrus that he kept on the down-low since he figured they would never be reciprocated, while Cyrus for the most part saw it as a strictly practical arrangement that mutually benefited them and their productivity. (At least that’s what he told himself since feelings are weakness and sentimental feelings doubly so.) The duo had been pretty careful to avoid any pregnancies but nothing has 100% effectiveness, so Aeon was just a perfectly-timed (for the drama obvs) accident to be conceived not too long before the Spear Pillar incident.

Later on, after leaving the Distortion World, Cyrus does eventually end up in a relationship with both Saturn and Archer though!

Callisto on the other hand was because before Spear Pillar Cyrus offered his Commanders a single “gift” on this world before the new world was created (aka wanting them to get all their foolish emotions/desires/etc out before focusing on the mission and to reward them for their hard work and loyalty). Mars asked for some cash for a shopping spree, Saturn requested to spend the final hours as he chose so ended up doing work elsewhere than Spear Pillar and Jupiter… wanted a piece of the action Saturn was getting to see what the fuss was about and since this was probably her only chance to. Cyrus complied (to her slight surprise) and she… did not see what the fuss was about… and then ended up with her own accident baby born in prison later on after the team was defeated because I just like soap-opera esque plotlines ok. But Callisto’s story is for another post haha.