disobey, defy, go back on, rebel, rebellion
叛 centers on turning against an obligation or authority: disobeying, defying, going back on one's word, or rising in rebellion.
叛 combines 半 (half) and 反 (oppose, return). The historical development is uncertain, but the components together suggest a split or turning away, fitting the idea of rebellion.
The left side 半 (half) and right side 反 (oppose) together suggest someone who is half-hearted and turns against their duty, like a rebel disobeying orders.
For ハン, imagine a rebel named Han who defies authority: Han -> ハン, and his rebellion is the core of 叛.