This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 殅 is uncertain. It combines 歹 (death, decay) with 生 (life, birth), but the original meaning and component relationship are unclear.
The left side 歹 suggests death or decay, while the right side 生 suggests life or birth. Together they might hint at something like revival or coming back to life, but the actual meaning is uncertain.
For ソウ, imagine a soul (ソウ) hovering between death 歹 and life 生, uncertain which way to go. Soul -> ソウ.