In Shingeki no Bahamut: Virgin Soul Episode 1, the main character is this 16yr girl who transforms into a powerful dragon whenever she gets too aroused. Or at least thats what it seems like so far. Has a brief process but likely to be much more in the series.
http://anilinkz.io/shingeki-no-baham...pisode-1?src=7 process happens around the 18:45 mark