This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
瓪 combines 瓦 (tile) with 反, which may contribute a phonetic element, but the exact historical development is uncertain.
The kanji visually contains 瓦 (tile) and 反 (anti-), but without a clear meaning, it's hard to form a reliable mnemonic. Perhaps imagine an anti-tile that refuses to fit in the roof.
For ハン, imagine a half-broken tile: half -> ハン, and the tile 瓦 is cracked by the anti- 反 force.