Usually a modern form influenced by Aidan, meaning “little fire,” though it also resembles Japanese name elements.
Kaidan emerged in the early twenty-first century as part of the great Caden/Kaden/Caiden wave that swept Anglophone naming around the turn of the millennium. That wave itself had uncertain origins — linguists and nameologists have debated whether it traces to the Irish surname Ó Cadáin (from "cath," battle), to a Scottish Gaelic source, or whether it was primarily a sound-driven invention that simply felt right at a cultural moment. The -aidan/-ayden suffix was extraordinarily productive in the 2000s, generating Jayden, Hayden, Braden, Zayden, and dozens more names built on the same sonic template.
Kaidan, specifically, carries an additional cultural charge for those who know it: it is the name of a central character in the Mass Effect video game trilogy (2007–2012), where Staff Lieutenant Kaidan Alenko is a thoughtful, telepathically gifted human soldier. For the generation of parents who came of age playing that series, the name arrived pre-loaded with associations of intelligence, quiet strength, and moral complexity. Game characters have been giving names to real children with increasing frequency since the 1990s, and Kaidan is among the more elegant examples.
Japanese speakers will also recognize a homophone: 怪談 (kaidan), meaning "ghost story" or "strange tale" — a coincidence that adds an unexpected layer of eerie literary resonance to a name that otherwise sits squarely in American contemporary naming culture. It is a small, delicious ambiguity that the right child might one day appreciate.