Close to Home

Once the other main quests have been done and you have finally decided the fate of the factions controlling the island AND Acadia remains intact (you didn’t complete Forbidden Knowledge, Search and Destroy, or chose the options that will cause the people of Far Harbor attacking Acadia), you can talk to Kasumi and help her decide whether to stay in Acadia or go back to her parents.

Whatever the decision, as long as Kasumi is alive and well, the quest will be complete and Kenji will give the location of his father’s stash that contains a lot of items and caps for the taking. The stash is locatedin the small storage shed outside the boatside near the family house.

Alternatively, if Kasumi is killed due to the attack on Acadia, you can still close the case by talking to the Nakano family. The quest will be completed by you’ll receive no other rewards.

Finally, you can also go back to Diamond City and talk to Ellie in the Valentine's Detective Agency. Talking to her doesn't yield any reward but brings a nice closure to the whole thing.