|"It'll be fine. Every cat knows that Emberstar's closest friend is Thistletail, in ThunderClan. If any cat understands that friendships don't stop at the border of a territory, it's Emberstar."|
|— Ryewhisker about Thistletail in Code of the Clans, page 12|
Thistletail is an ancient ThunderClan cat. In Code of the Clans, Thistletail is mentioned by Ryewhisker, while he is talking to his mate, Cloudberry. Ryewhisker tells Cloudberry that Thistletail is Emberstar's best friend, despite Emberstar being RiverClan's leader. Ryewhisker uses the bond between Emberstar and Thistletail as an example that Clan boundaries don't separate friendships.