Each item links to the page with the full rules and the official sources. Items marked "announced" have not taken effect yet.
Jetstar Airways (JQ) says that from departures on February 2, 2027, all fares include one bag that fits under the seat (40×30×20cm); an overhead locker bag comes with a paid option or some bundles (up to 10kg each).
Japan's Ministry of Land, Infrastructure, Transport and Tourism (MLIT) limits power banks carried on board to 2 per person (160Wh or less each), and asks passengers not to charge power banks on board or charge devices from them.
From July 1, 2025 (trial): Shinkansen: deck baggage areas without a reservation for bags up to 160cm
JR Central and JR West let you use the deck baggage areas of cars 3, 5, 7, 9, 13 and 15 on 16-car Tokaido and Sanyo trains without a reservation for luggage up to 160cm in total (a trial for the time being).