⺀ is a Unicode character at U+2E80, named CJK Radical Repeat. It is not a Chinese character in ordinary use, and it is the first character of the CJK Radicals Supplement block.

Every other character in that block depicts a shape that also exists among the unified ideographs, so each of them has an ordinary character a reader can use instead. ⺀ does not. Unicode records no cross-reference for it, which makes it the one character in either radical block with nothing to point to.

The CJK Radicals Supplement block holds the radical shapes that the Kangxi Radicals block leaves out: variant forms, simplified forms, and the shapes a radical takes in one position rather than another. Unicode annotates ⺀ as a variant of Kangxi radical 3, the dot, encoded in the other block as ⼂.

Its purpose is the same as that of the Kangxi Radicals block. A table of radicals is a list of abstract indexing elements rather than a passage of text, and giving those elements their own code points lets a font apply chart-specific shapes and spacing without disturbing how the same glyph is drawn in running prose. The block also serves round-trip compatibility with older East Asian character sets that had made the same separation.

Neither purpose involves writing words. Because ⺀ has no counterpart among the unified ideographs, there is no ordinary character it can stand in for, and no context in running text where it belongs.

⺀ carries no decomposition of any kind. No normalization form — NFC, NFD, NFKC or NFKD — will change it, and none ever will, because normalization is stability-guaranteed and decompositions are not added to existing characters.

For the other 113 undecomposable characters in this block, that permanence is a practical trap. Someone copies a radical glyph out of a chart, and the ordinary character it resembles never matches it again, in any system, indefinitely. ⺀ works differently. There is no ordinary character it could have folded into, so a string containing it will never match anything else, and nothing was lost in the copying.

• ⼂
• Kangxi radicals
• Unicode normalization

• The Unicode Standard, Chapter 18: East Asia — defines the Kangxi Radicals and CJK Radicals Supplement blocks and their intended use
• Unicode Standard Annex #38 — the Unihan database, including the radical-stroke indexing this block supports