Kaiba is the only series i've watched where it felt like the female lead (Neiro) wasnt hollowed out in the presence of her 'love interest'. The romance in Kaiba is so non traditional I struggled to think of it as a romance because it's so atypical (i also don't like describing it as a romance because that flattens the actual story). Neiro is actually given MORE depth than Kaiba when they meet in the flashback, and she actually feels like a compelling character. The series refuses to make her reliant on Kaiba's presence to achieve things for herself.
The series also refutes the message that you NEED someone else to complete you. "No one can fill the hole in your heart" symbolized by the ever gaping hole in Kaiba's chest. The hole only disappears at the end, once he's confronted himself and his trauma, not because of some union between him and Neiro. Neiro herself had to confront her own demons prior to that.
The relationship also isn't purely 'romantic' in the traditional sense as it focuses on their friendship and emotional bond before developing it into romance. Even at the point where Neiro asks Kaiba to 'hold her' its not a particularly happy moment. She is sad and lonely and has lost her family, having no one who she feels truly cares for her.
The only kiss we get from them is super brief and in a flashback. Their bond goes beyond just a desire for one another. It is obvious they love each other, but it's a transcendent kind of love that goes beyond physical bodies and gender and even time or place. For me that's what made it so meaningful. They allowed it to be messy and undefinable. They allowed both characters to breathe independently from one another even though they are important to each other.
