Undoubtedly, my favorite couple in all the Buffyverse, until Spike and Buffy get together. But Spike and Buffy was tormented and insane. Where Oz and Willow are innocent and sweet.
From the first time Oz lays eyes on Willow, tingles are to be had. And the first thing he says about her is
Who IS that girl?
And of course up until they officially meet that becomes he trademark catchphrase. He is entranced by her. To Oz, Willow is beautiful and mysterious, and someone he genuinely wants to get to know better.
The first time they actually meet is in the second season’s What’s My Line during career day. Where they were the only two students smart enough to be recruited by a secret government agency, it’s clear that they have intelligence in common, if nothing else. Oz offers her a canope. It may be love at first sight, even if they don’t know it right away. But after Oz gets shot during the second part of the episode during the career fair, Willow takes part in helping Oz recover and opening his animal crackers. That was a defining moment in their relationship. It’s the single moment when Willow gets caught off guard, and Oz swoops in with a compliment, showing different sides to both characters.