You look happy today, for some reason.
When you were born one hundred years ago today, I was happy. Happy birthday.
Nothing happy has happened to me lately.
This is a single kanji with an い on the end, meaning you know it's probably an adjective. What's the adjective form of glad? It's also glad!
Whenever you're really glad to be alive, you look up at the sun's rays and sing, "Ooh, rays (うれ), I'm so glad you're here!" Then your Uncle Ray comes dancing into the room and sings back, "Ooh, Ray is happy you're happy!" The sun's rays and Uncle Ray both make you really happy.