Rido & Juri

Background
Rido was in love with Juri though little is known of their relationship beyond the fact that Juri rejected him and chose Haruka instead. All 3 were siblings.

Rido asked Yuki in Chapter 43: "Juri, why am I not good enough? I love you so much that I feel like eating you whole.".

Rido seemed to be obsessed with Juri and its clear that he lusted after her. In spite of Rido's love for Juri and the following rejection, maintained an amicable relationship with Juri and Haruka and they never suspected what he was capable of until he stole their newborn baby, Kaname Kuran. Following that incident Juri maintained a great anger at her eldest brother but held no other hostility towards Kaname.

It can also be noted that the last Kanji in Juri's name, Ri, is the same one in Rido's son's name, Senri. This hints more at the allusion that Rido still loved Juri even after her death.