The Merman's Children.
(i) In historical fantasy set in the fourteenth century, as in hard sf set in the future, human beings interact with other intelligent species.
(ii) Magnates of the Hanseatic League (p. 126) become more powerful than kings like their successors in the Polesotechnic League which was modeled on the Hansa.
(iii) Catholics and Orthodox of different rites survive into the periods of the Polesotechnic League and of the Terran Empire.
Looking not forward but backward, a provincial ruler in the fourteenth century is protected from evil spirits by "'...a fingerbone of St Martin...'" (p. 132) Bishop Martinus was a prominent figure in the earlier period of Ys. The fingerbone is carried in a cross on which:
"A crystal covered a hollow theren." (ibid.)
The evil spirits include a vodianoi:
as bulky as three war horses;
with moss and weeds growing on him;
glowing red eyes.
Explorers find similar beings on other planets in the future.