OK, well out of the 3 kamigawa dragons that show up in the books or short stories, I'd have to nominate Keiga, the Tide Star as not being terribly flavourful. I mean, Jugan, the Rising Star strengthens the monks after it dies, and Yosei, the Morning Star manages to hold up a swarm of Akki even after being wounded by O-Kagachi, both of which kinda fit mechanically. But the only thing Keiga does after getting the crap beaten out of it by Hidetsugu and his Yamabushi is provide a tasty snack. I mean, sure, it has a good, blue ability, but it doesn't have any particular flavour to go with the story.
Hidetsugu did have the help of a certain band of Kumano's Pupils, so Keiga's ability wouldn't have triggered anyways. The same would have been true if he had used any Yamabushi magic as demonstrated in Yamabushi's Flame or Yamabushi's Storm
2. Scrying Sheets
3. Adarkar Valkerie
4. Haakon
5.-10. is a large tie between all of the other garbage rares in CS.
Hidetsugu did have the help of a certain band of Kumano's Pupils, so Keiga's ability wouldn't have triggered anyways. The same would have been true if he had used any Yamabushi magic as demonstrated in Yamabushi's Flame or Yamabushi's Storm