I am currently working on this image in Krita:
The ninja is on some sort of roof, I am a bit unsure about what to do next.
I like the idea of making it a team of ninjas artwork. Like three more ninjas in the picture, maybe each having or holding something that visually puts them apart from the others.
As for the background, the roofs of an ancient temple city sounds cool I think.
Time of day: Night time with a full moon above.