They're perfect pillows !
I really like the thing with Nanoha, they live together, they sleep together, rise a child together... They didn't leave any challenge to the doujinshis ! I haven't read Vivid (I did and then pause it because there were so many characters and they're all so alike that nothing made sense anymore) enough but I bet with Vivio it will be even more obvious.
I want someone to ask them "Are you married?" and see them like "OMG no! what make you think that?!"
I like this kind of story too but someone should write a story where they are a little older so the relationship goes somewhere ViHart is great but under appreciated.
I know Einhart is super shy and socially awkward at times but she seems incredibly tsundere in the first few pages.
Oh and Fate's reactions are gold XD
This is part of the MekiMeki Omnibus 1 btw. I don't know if the Magical Valentine Kiss is as well, cause there's a chapter that's titled A Magical Girl's Valentine's Day Kiss and it could be shortened.