big
昄 centers on largeness or bigness. It is a rare kanji whose core idea is simply 'big'.
昄 combines 日 (sun) and 反, but the exact historical origin is uncertain. It may have originally expressed the idea of something large or expansive like the sun, but this is speculative.
The sun 日 is big, and 反 looks like a hand measuring something large. Together, 昄 means big.
For ハン, imagine a big hand (ハン sounds like 'hand' without the 'd') holding the sun: hand -> ハン, and the sun is big.