Hi, I encountered this topic and Nicky's tatoo is quite interesting...I read it in a Japanese book (actually the book's a translation of the excerpts from Nicky's diary, the author of the book had read Nicholas's diary in Moscow around 1983-1984).
According to the book, Saigo no Russia Koutei Nicholai Nisei no Nikki[The Diary of Nicholas II, the Last Tsar in Russia ] written by Koichi Yashuda (Tokyo: Asahi Sensho, 1990)
pp. 26
Nicholas must have known that there was an excellent tattooist in Nagasaki. As for "tatoo" there was a scene where Loti got a tatoo of peony on his chest, in a book, Okikusan written by Pierre Loti, which Nicholas had read on the day before he arrived in Nagasaki.
[...]
When I encountered this description about his tatoo, I wondered if he had kept [...] the tatoo which was done in Nasasaki as a token of his visit to Japan until he was killed in 1918 and felt surprised but quite impressed. [The image of] Nicholas got much closer to me.
[end of quotation from the book. Sorry for my rough translation...]
I've been wondering, if his tatoo was inspired by Loti's Okikusan...
aya-anya