When Arata accidentally steals Lun Lun'sFirst Kiss, she starts making a big deal out of it...which, after a moment's hesitation, leads to him proposing on the spot. Lun Lun is rendered speechless, though she does let him off the hook.
Arata: I'll take responsibility. I'll dedicate the rest of my life to making you happy.
Upon being informed that Chris is a girl...Suzushiro doesn't care. Suzushiro has devoted herself to Chris her entire life, not to "the prince," so Chris is still number one in her heart, and Suzushiro will always be at Chris's side, whether friend or lover.
This one's more subtle, but the sheer strength of Liliana Lun Lun Guenther's feelings has to count. Liliana falls in love with Arata, and because of this she: gets back up against impossible odds after Angela uses a frighteningly damaging technique, decides that her loved one is more important to her than the prince after previously criticizing her siblings for marrying "beneath" them (that Arata secretly is the real prince notwithstanding), and wears her school uniform for her sex scene just to have something in common with Arata.
Riko overcoming all of her mental barriers and lack of confidence and fighting as Liesel for real, instead of behind a mask...just because she's sorry that an earlier fight of hers ended up hurting Nodoka.
In Shizuka's backstory, we learn that Nanae intentionally put a mental lock on Shizuka's Beast Princess heritage. But Shizuka's feelings for Arata are so strong that Shizuka becomes feral and out of control...and even feral she thinks of protecting Arata first.