Ask from @sarellathesphinx !
Rifra's favorite part of Estinien is his empathy. It's a big part of why she loves him in the first place, especially given how the two of them have had several similar experiences together, from becoming marred by vengeance, having their personal autonomy threatened by the beings that haunt them (Nidhogg and the Inner Beast), etc. Estinien is the one person that can understand her on a personal level, the one person she can feel completely vulnerable around.
Estinien's favorite part of Rifra is just how different and unique she is compared to everything he's known growing up in Ishgardian lands. He's never seen a viera prior to Rifra/Seren, let alone someone who's extremely outspoken and also just... openly promiscuous. Him being near her, whether it's during Heavensward or in general, makes him experience so many new things and open his eyes to so many new perspectives that it just draws him to her.
AS FOR THE CUTEST PARTS
Rifra loves Estinien's ears! What other purpose do elezen ears have other than to be bitten? And there totally isn't another subconscious thing that influences him to be drawn to biting his ears often, absolutely not.
As for Estinien, he thinks his viera nose is the cutest charm point! The way it darkens near the tip gives him so much cute aggression. He boops it often and it's his favorite place to kiss him on.
