http://yokai.com/ is a site dedicated to all forms of supernatural spirits from Japanese mythology and is a wealth of ideas for something new to throw at your players. I use it a lot myself as I find the old L5R everything malignant = Shadowlands is rather boring and I've used it to throw a curve ball more than once.
See also: https://en.wikipedia.org/wiki/List_of_legendary_creatures_from_Japan
http://www.samurai-archives.com/ a good wiki/clearing house with a lot of information on samurai culture throughout history from banners, to mon, to house codes. Pretty much anything a GM needs
an Index of Kamon (house crests) that might inspire designs for Minor clans: https://doyouknowjapan.com/symbols/
Authors: Stephen Turnbull is a historian who has done a massive amount of work on samurai culture in various areas and has a rather large archive of books one can go look for further inspiration ( I have a large part of his writings, which I use). his bibliography is listed in the following article https://en.wikipedia.org/wiki/Stephen_Turnbull_(historian)
Edited by TheWanderingJewels