Kaius Starling was used to being the second choice in everything. Youngest child of his parents, spare to the throne behind his twin sister Charlotte. The universe had a twisted way of making him the incorporation of that position. He was second in everything, including Leah Willows' heart.
She was another person swept away by Charlotte, both considering each other soul sisters. Kai was happy for that, happy to watch his sister having someone to lift the weight on her shoulders, but a small part of him, the ugly voice beneath all wit and charm, wished to take all of that girl and keep her inside his heart.