Do you have a rough ideas, at least? That way, you can set which way the story goes..BTW, do you free run? That's freakin cool. I tried it my self, but got quite beat up after an accident....  "Thou art I. I am thou. Thou shalt be blessed when creating Personas of the Headphone arcana....."

I think what you have is a very great idea .... most sport animes focus on friendship and working together but if you also look they always take the sport to a grerater level running accross the football field at light speeds or slammng a ball to the point that it destroys the entire stadium. So what I can reommend is create a character in your head then imagine all the cool things he can do if he was was or if she was the best free runner , then think about all the hardships of free running , like keeping fit or facing your fears, I guess what im trying to say is listen to music watch some anime about sport and let your mind exaggerate everthing if its cool and impposible you are on the right track ( pun not intended)

So are you going to give the characters powers and special abilities or are you keeping it reallistic?Or are you going to exaggerate stuff to make it cool? "Thou art I. I am thou. Thou shalt be blessed when creating Personas of the Headphones arcana....."

to me its best to exaggerate the only problem is making sure the reader can define how the power looks and works but if you can get it right your Manga is gonna rock

why don't you just jot down some ideas first and then choose which one you want which corressponds to the ending

story like this:There is a fame guy who traied asparkour student,uses his knolige on eveding fights and running from dangers appear at school,street,buildings.You can think of even that he can be envolved withcriminals who are traing to get rid off him and what?He is doing his stuff affcoarst and with martial arts will be even intersting