> A quick google suggests ~18%

FWIW, this figure looks to be the fraction of 20–69 year olds in the entire population who are unemployed[0]. Referencing the official definitions[1], the standard unemployment figure of 2.6 (as of 2026-02) narrows that denominator to people who are receiving wages or actively looking for work.

> which naturally could be shifted by incentives like money or training.

From the above, 18% seems like the wrong number to look at. Heck, why not quote 38.1%, since it captures everyone who can legally work (including 15 and 90 year olds)?

IMO, the base population we want to look at is people who actually want a job, which is captured by various Labor Underutilization (LU) metrics. These all hover around 2.5–6.0% according to public records[2], and are also defined in the official docs[1].

[0]:https://www.stat.go.jp/data/roudou/sokuhou/tsuki/pdf/gaiyou....

[1]:https://www.stat.go.jp/data/roudou/pdf/hndbk5_2.pdf

[2]:file:///var/folders/96/k0p95wxn7sg5_xjnv5n233bc0000gn/T/gaiyou-1.pdf