Japan's legal system barely does anything to these types of people. And five years is the most common span of time for people like her mother stay in prison.
"For example, three quarters of all defendants in r-pe cases were sentenced to prison terms of 2 to 3 years and about one half were granted suspensions, although the statutory provision for r-pe is imprisonment for 2 to 15 years." (
https://www.ojp.gov/ncjrs/virtual-l...japan-unafei-united-nations-asia-and-far-east )
Assault: This may entail imprisonment with work for not more than two years, a fine of not more than JPY 300,000, or misdemeanor imprisonment without work or a petty fine. Injury: This may entail imprisonment with work for not more than 15 years or a fine of not more than JPY 500,000.
(
https://resourcehub.bakermckenzie.com/bg-bg/resources/fighting-domestic-violence/asia/japan/topics/5-prosecutorial-considerations#:~:text=Assault: This may entail imprisonment,not more than JPY 500,000. )
Distribution, etc. of Child P-rn-graphy. 1. A person who distributes, sells, lends as a business, or displays in public, child p-rn-graphy shall be punished with imprisonment with labor for not more than three years or a fine not exceeding three million yen.
(
https://www.ilo.org/dyn/natlex/docs/WEBTEXT/53924/65175/E99J#:~:text=Distribution, etc.,not exceeding three million yen. )