I'll use spoiler tags just in case, but the non-spoiler Tl;Dr is it's more than that. It's not about lust or desire.
It's about belonging, being valued not for what you can do, but for who you are and having others care about you, even being willing to sacrifice themselves in a heartbeat to save you.
I really like Toto, he reminds me of Helck in many ways, he's someone that doesn't pander to titles or accolades, he's a hero because he cares about others and values every single person he comes into contact with no matter how large or small a character they are.
Some of it has already been shown/hinted at.
Back stories of Ceil, Goa and Anemone.
As you've probably picked up on from Goa trying to use her powers to convince Toto to love her, none of them have had very nice lives.
Ceil has spent her life training in order to earn her father's love, but she has no friends, everyone around her whispers about her when they think she can't hear them, calling her "fake" and stuck up.
Anemone was an orphan on the streets who started off with stealing just to survive, she's been alone for a very long time and ended up in the assassin gig because she showed potential. She actually donates her money from her contracts to orphanages. she even volunteers herself from time to time, helping to feed and care for children.
Goa's powers made people terrified of her, even as a child, so no-one wanted to be her friend or be near her, even when she tried to help people.
None of them have ever had someone care so deeply about them just for they are.
Where things start to change
It isn't that far ahead (around chapter 54 if I remember correctly), but there's an enemy the three of them can't beat and just as they think they're finished Toto shows up and one-shots him, only to be surprised when all three jump him for a hug.
Not long after that there's some magically induced dreams where they believe they've killed him and are living in the aftermath, only to realize that his death is hollow and they were happier in a party with him and the others.