It is pretty sweet. I like how it even shows in the way they're drawn, with their bodies fitting perfectly together like puzzle pieces during their frequent hugs, as described here >>112281357
Early on in the series I was seriously wondering why Sylvia even puts up with Wander, even though Wander's compulsive need to help everyone kept dragging her into all kinds of weird and dangerous situations. Sylvia was introduced as a cynical, tough fighter who was pretty much the opposite of Wander's cheerful pacifism, and a bunch of episodes showed that she tends to gravitate towards badasses, bullies and antiheroes. It seemed like she didn't have anything in common with Wander. And since he kept getting her into trouble on a constant basis, it made me wonder why doesn't she just ditch him.
Eventually I started to think about Wander's tendency to seek villains, hang out with them, and try to befriend them. Maybe Sylvia was one of the villains he met at some point, but Wander's influence reformed her? If he helped Sylvia become a better person, that would explain why she values him so much and wants to stay in his company despite their seemingly clashing personalities and all the headaches he keeps causing her.
Felt pretty excited when I finally reached the episode where that was confirmed; I love stories that involve villain redemptions. I just wish there could've been a chance to see a little more about how they initially became friends.