Shinobi no Hana ~Kunoichi Shimai no Chousen~

Main character is an unsuccessful detective who struggles to catch a gangster girl.
One evening he hears a rumor that the legendary thief is going to rob the art museum at night. When he arrives at the destination he finds there the Kaito group of female ninja who accumulate wealth to revive the ninjutsu art. The mystery gradually deepens.

[From vndbreview]