From June 2, 2025, it will be possible to order pickup of empty containers from Cyber Port at Aomi A4 Terminal in Tokyo Port and Honmoku BC Terminal in Yokohama Port.
The forms for both terminals are as follows. For details of operation, please refer to this.
Empty Container Pickup Order
container cargo delivery slip

The Ministry of Land, Infrastructure, Transport and Tourism also introduced this issue in a press release.
https://www.mlit.go.jp/report/press/port05_hh_000380.html