Shin Shirayuki-hime Densetsu Prétear, Luck & Logic Recommendations
Both involves a main character that uses a person to transform and gain a power.
Himeno can transform with multiple guys who are magical knights. Whereas, the characters in Luck & Logic transform with one partner and the transforming partners are goddesses.
Himeno falls for one of the knights and the main lead in Luck & Logic has a partner with feelings for him.
The characters in both of these shows have to fight off bad forces that show up.