Aoba's ending. She's my favorite character along with Jun (she grew on me) but by the ending her personality has done a complete 180 turn until she's about || far from being a Yamato Nadeshiko. Obviously she can't stay a Broken Birdjerkass in her ending but... couldn't she have stayed a little bit evil?
Seems Fridge Brilliance to me: she was not a "natural" tsundere, she was just like a dog that tries to bit everyone because it has received too many beatings: she was thrilled when she finally got someone to treat her kindly. After Tsukasa confesses his love for her, she gives him her heart completely and unconditionally, feeling wanted for the first time of her life.