Well, I can tell you I became shipper of that pairing just because of one fanart xD
But to explain it in other way, I think that they could work together becauseee... they are different from each other... She has things that he doesn't have, and so in other way. He would be an accelerator for her, while she would be decelerator for him... so many things which they could fill for each other
Beside, I think he is one of the captains that visits 4th division the most... yknow, fighting, then there are the wounds and then he goes to 4th division. So, connection between them two really exist.