Help to find anime

I need help to find an anime that sadly I have little information about, but recently I watched the opening on a store:
\- The opening focused on a girl and a boy, they seemed to be around middle school age.
\- It also showed them on primary school, at least the boy, with another group of kids. It seemed like a flashback though.
\- When they were middle school age they fought with swords.
\- The boy who seemed to be the MC had brown hair, not long and wasn’t
wearing glasses. The art style of his hair I think that it was similar
to Code Geass (the hair strands).
\- The last frames of the opening were just that boy wearing a white
shirt, but during the rest of the opening he was wearing different
clothes, more like combat clothes.
\- It didn’t seem to be a recent anime possible from the early 2010s. I
saw it played alongside Sket Dance and FMA: Brotherhood ops and the
animation seemed to fit those years, if not earlier.
\- In the opening I watched the tittle appeared written in kanji and seemed long.

View Reddit by RegularOutcomeView Source