The MC said Japan is peaceful they don't need ninjas but there is a lot of situation they needed:
Against Yakuzas
Cult or money lecher sects
Son of influential people that mess around and being protected, or how can they ruin your life by reclaiming your right by being victim of some abuse (legally you can be sued if you damage the image of someone/company that has some prestige)
The ignored RAPE culture
The weird case of negligent parent or abusing relatives
Bullying
The hardcore ignored workflow over exploitation alias "Black Company"
The Stalkers mostly the crazy ones
Infidelity or the famous NTR, or just check your partner has no syphilis or just a sociopath
The child prost... rental services and mostly the extortion by some of the parts involved
The Rental Girlfriend and the weird case everything goes bad (extortion, infidelity, stalking, prostitution, proxenetism, etc)
Company espionage or sabotage and extortion, or negligence against customers and neighbors
(I ignored the runaway people, missing people, homeless, neets, suicides and social suicide clubs, and people don't want to be found, because those are things that a ninja cant solve in a positive way for the society)