That is… the ‘Youth 18 ticket’. It requires neither that you are youthful nor 18… but it is a ticket.
It is a discount ticket that gives you unlimited travel on Local JR trains for 5 days within a certain time period. It’s sold and valid three times per year, coinciding with the school holiday periods. (Click here for more info)
It costs 11,500 yen, so that works out at 2,300yen per day for unlimited travel. Also, it’s totally transferrable. Give it to a friend, your mum or your dog and they can use it to ride the trains for a day (well… maybe not the dog).
The local JR lines are slower than an express or Shinkansen… but you get to enjoy watching the hills, rivers and sea roll past while making stops at the smaller stations you’d never see otherwise.