Japanese just don't know or are too lazy to repair a flat tire.
There's this 60+ year old man in my neighborhood doing it out of a shed-like shop and he's always busy.
I don't think he's cheating (walking around with a needle/pin puncturing tires in the neighborhood at night).
He works five days a week from ten to six and goes on onsen trips at least once a month. Not a pensioner yet.
Think about it - He charges Y1,050 to fix a tire (front or back) and Y100 to pump some extra air.
How many "punku"and "kuuki" is that to make the equivalent of say... an eikaiwa salary? You did the math already?
No qualifications necessary and you'll be self employed.
Buy your used bicycles from the local government (the ones removed from the station but have never been picked up)
and sell them for triple the amount you paid and you got yourself a nice little extra going as well.
Initial setup cost: Y740 for a repair kit including spanners and some rent for the shed.
Learn more "tricks of the trade" and you'll be able to expand your business in no time.