Answer
Clannad is the correct answer. Mai Nakahara has performed theme songs for several anime series, including Full Metal Panic!, Toradora!, and K-On!. However, she has not performed a theme song for Clannad. The opening theme song for Clannad is "Dango Daikazoku" by Lia, and the ending theme song is "Chiisana Tenohira" by Eufonius.