What ㌥ means
It writes デシ, the Japanese form of metric deci-. Deci- means one tenth of a unit. The square packs the two Katakana signs—Japanese syllabic characters—into one character-sized cell.
Older Japanese character standards used squared Katakana for unit names and other short labels, giving each a full cell beside ordinary text. Unicode preserves these forms for compatibility; styling ordinary Katakana into a square allows more flexible wording when available.
Use ㌥ when fixed-cell Japanese typography matters; plain デシ reads the same in ordinary text.
A font without ㌥ may show a blank box; デシ preserves the reading.
Don't confuse it with
4Questions people ask
1Why does ㌥ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
How to type ㌥
㌥\3325Codes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.