This seaside retreat, where the Nakano family lives, is right at the very edge of the Commonwealth. Since making a name for yourself as a Diamond City gumshoe, you've left yourself open to the punishment of requests from all kinds of people, including the Nakanos, who have misplaced their child and expect you to find her. Their adult child, who is perfectly capable of making her own choices and going wherever she pleases. Even if those choices and places entail rerolling her identity as a synth, which is a fad that is sort of like 'going emo', but for 2287 CE.
I did decide to go find out where Kasumi went and how she was doing, but I did it for the thrill of adventure, and not to manually correct Kasumi's fate. She has every right to pursue whatever life she wants, even if that pursuit is stupid and sucks ass.
Just so you know, she's not a synth (if you don't believe me, just save your game, blast her between the eyes, and search her corpse for a synth component), although Kasumi herself is hardly shocked at all when you don't even have to tell her twice. She's kind of relieved, because the synth town of Acadia is hard-core lame, and she's a little bitter about having come all the way out here for a place with no running water and no shitters. Which are both pretty important for humans!
Anyway this is the pretty powder room she left behind to hang out with DiMA, the 6-ft tall, fragile, leathery, synth cult leader freak who looks like Jean-Luc Picard with a bunch of Edison bulbs sprouting out of his skull. It doesn't take a ton of convincing to get Kasumi to return to this cheerful coastal haven, where the comfort of this shitter awaits. But not before Kasumi offers, out of nowhere, to personally destroy DiMA's reputation and burn Acadia to the ground.
