This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
祻 combines 示 (altar, spirit) with 固 (hard, firm). The exact historical development is uncertain, but it likely relates to a ritual or festival concept.
The left side 示 suggests a ritual or altar, and the right side 固 means firm or solid. Picture a solid, firmly established festival or ceremony.
For コ, imagine a child (子, こ) participating in a firm, traditional festival: 子 -> コ, and the child helps make the ceremony solid.