User blog comment:Skeith9/Heroic Spirits Speculation/@comment-24762556-20140624072224/@comment-1458758-20140625122143

Well Moby Dick is noted as a Phantasmal Beast of the highest order even in the normal Nasuverse, so you could be in luck.

Also, the thing with most of these, as Rin notes at the start of F/SN is that even fictional people can be called forward if their legend is strong enough.

So Frankenstein, Jekyll & Hyde etc. I count under that banner really.

Speaking of people you'd plan to write, I actually wanted to make Captain Nemo, who is actually Robert Fulton, the man who inspired the character.