Since when do people date versions of themselves?
This is just a Thing I’ve Noticed About Life, but actually a lot of first loves/relationships that I’ve known are people dating versions of themselves. Which makes sense—as you first become adult-ish, you look to the world for validation of who you are.
Later on you realize that you can be a lot better off with someone who has complementary personal qualities and strengths rather than the same ones. It’s still got to be someone who’s similar enough to understand you, of course.
(I don’t actually see Harumin and Sayaka being so fundamentally similar, though.)
... I agree with complementary personal qualities; different yet those differences can be both foil/improvement for the pair. Crossover, huh? In that case, the craziest (or sanest, in this instance of crossover) I could think of would be Matsuri and Sayaka.
IMO they are both whom I consider "codebreakers" in the sense that they know how to read people and accurately guess their intentions. The difference would be in the execution of that intuitiveness. Matsuri is almost sociopathic in her approach that she'd definitely use that knowledge to her own amusement or advantage (thankfully, she'd use this talent finally for good against Mei's idiotic decision to almost marry Udagawa). Dear Sayaka could take some cues from this high-functioning sociopath pinkette that it's okay to sometimes take risk sooner and not later. Conversely, Matsuri could take cues from Sayaka's finesse laidbackness instead of grabbing someone's boobs from behind (which Matsuri did to Harumi) or being overly sensual (sexual?) when expressing her lovey dovey emotions to another girl (Sayaka's confession was smooth and gentlemanly, Matsuri is like this Jack Sparrow who'd seduce and bed an unsuspecting lesbian virgin).
Or something like the tandem of Holmes (Matsuri) and Watson (Sayaka)... They'd most probably repel each other at first (with Watson being weirded out by Holmes' unorthodoxy), but it'd be the case of frienemies turning to lovers...
Goddamned, I'm just frustrated that Sayaka Saeki's not getting any and obviously hurt in the canon series.