I was reading it a few years back, but it wouldn't update past chapter 4 or so, so eventually I forgot about it. Basically it begins with the protagonist meeting this mysterious boy who pretended he could move the fireworks with his 'magic' by like waving his arms around 😀 And then they somehow meet a few years later and the dude who had protag fooled with his 'firework-bending magical powers' turns out to be working at a shop where they make/sell/set off fireworks, and if I recall correctly, the people who worked there liked to refer to themselves as pyromaniacs?
Thanks in advance~ 😛

Oh nevermind, I just managed to find it myself XDDD Setsuna Graffiti, right?