Hassan of Serenity, while she retains the title of Assassin in our system, is quite clear in Fate/Grand Order that she no longer wishes to kill, and we honor that—although I suspect that Serenity still reserves the privilege of scaring the crap out of people >_> We're not entirely sure what she gets up to, if I'm honest. Magical combat with other Heroic Spirits is a somewhat different matter, although that's a problematical one too—that gets into our general bad feelings about the corporate Fate/ empire, and I won't get into that right now.
We very much would like to educate ourselves properly on her people, the Nizari Isma'ili state founded by Hasan-i Sabbah in the 11th century C.E., centered chiefly around a cluster of strongholds in Persia. The chief of these was Alamut Castle in the mountainous territory just south of the Black Sea, in what's now the Qazvin Province of Iran. This remarkable political entity managed to retain its integrity for about two centuries despite its minuscule size compared to much more powerful neighbors, partly through selective terrorism and assassination. They came to be known as the "Order of Assassins" and the "Hashasheen" and from what I can tell, they've been a prodigious inspiration in Western culture for the production of utter bullshit. Marco Polo spread a bunch of crap, it got picked up and romanticized by later writers, and now you can play a bunch of video games (I haven't played a single one) inspired—in the very loosest and most generous sense of "inspired"—by the people whom Hassan of Serenity once helped to keep safe, as a trained assassin.
I think she might actually be curious about "Assassin's Creed", if I'm honest.
Imagine being from Persia in the 12th century C.E.! I have a difficult time imagining it. Unfortunately, so does Serenity herself; her memories are extremely cloudy, and to be honest we're not sure how any of our Heroic Spirits have come to feel that they have such a secure lodging with us. We're not exactly mages. In any case, doing homework about Serenity's people (and about all our historical and semi-historical introjects) is one of the many lengthy tasks ahead of the Pnictogen Wing.
(sighs) how we'll manage, I don't know
~Chara of Pnictogen