Yes, I admit - I stole that idea from never ending threads from Naruto-section, but I thought one in SR wouldn't harm anyone.
Let's get to the point. Let's assume that Flag will happen and Harima and Eri will become pair (and I bet lot's of people find it as undeniable truth that it will happen)...
.. Then what ?
It's not like they have similar interests, moreover Eri is quite a rich girl so her parents might not approve of her decision (they were making omai's for her with strict regulations). After they end school, it seems they will try for different colleges/universities/academies/whatever they have in Japan, so they won't be able to meet so often. They also go completely different paths in life (it's not like it destroys relationships, but doesn't help too). Furthermore, let's face it, both of them are quite selfish - they are bound to quarrel a lot.
In summary, I never were a flag fan because this relationship has no future (I know, love can overcome everything bla bla bla) and I still think it won't work.
Please, prove me wrong :)