Complex sentence: She's a rich, yet desperately lonely girl who has lost all hope; she falls in love with Kaito to the point that, in Lucia's perspective, he has forgotten his mermaid love completely, and is desperate that he return her feelings.
Split into simpler sentences: She's a rich, yet desperately lonely girl who has lost all hope. She falls in love with Kaito, to the point that, in Lucia's perspective, he has forgotten his mermaid love completely and is desperate that he return her feelings.