Convenience stores and even ¥100 shops sell chargers. The ones at the ¥100 shop are about ¥770 for USB C (less for A), and the ones at the convenience stores are twice the price or more. Most stations also offer portable charger rentals, too.
When I first moved here, I brought a power strip from my home country and just used that with an adapter. It worked well but YMMV.
Hope you have a great trip anyway.