A follower of Christ
Kirstin is a Scandinavian variant of Christina, ultimately derived from the Greek name Christos. It has been used in English-speaking countries as a more distinct alternative to the more common Kirsten or Kristen.
Less common today
Kirstin isn't in the latest US Top 1000. It last peaked at #565 in 1990.
Grammy-winning singer and member of Pentatonix
German professional tennis player
US births per 5-year period, 1990βpresent (SSA data).