I think Himmel is a phenomenal character because we don't see him too often. He is such a purely good (in the moral sense) character that if he were the main character and he was on screen all the time, we would probably get sick of him. Instead, we see Himmel almost entirely through Frieren's memories. This means that we only see the important bits when Himmel was doing something silly or profound (sometimes both). It is like watching a highlight reel of an athlete, you only see the best moments of their career rather than all the more mundane moments or the times they struggle.

Really loving this adaptation. Himmel won the manga popularity contest, but I am so glad to see his popularity being carried over to the anime watchers as well.

It might just be the first sentence. He focuses on his appearance, so Frieren is more likely to remember what he looked like because it was part of his character traits.