This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
腅 combines the flesh radical ⺼ with 炎, but the exact historical development and original meaning are uncertain.
The left side ⺼ suggests flesh or body, and the right side 炎 suggests flames. Without a clear meaning, you might imagine flesh being cooked over flames, but this is only a visual mnemonic.
For タン, imagine a tan piece of meat (⺼) roasting over twin flames (炎): tan -> タン.