I drew a manga of Light and L as kids. I feel like they both have this similar kind of coldness. L only cares about interesting mysteries; he doesn't dislike Watari's concern for him, he's just genuinely confused by it and only asks questions about things he actually finds interesting. Light doesn't hate his cute, innocent little sister looking up to him either, but he only cares about 'big important things' and can't understand why she'd admire him for such tiny, trivial stuff. They're two bored kids, just waiting for the day fate finally brings them together.