Where the Letter H Breaks the Pattern
Most mathematical styles run A to Z in one unbroken block, but not all of them for this letter. Italic small h is â (U+210E, Planck Constant). Script capital H is â (U+210B, Script Capital H). Fraktur capital H is â (U+210C, Black-Letter Capital H). Double-struck capital H is â (U+210D, Double-Struck Capital H). These were added to Unicode in the Letterlike Symbols block years before the mathematical alphabets, and the later block left a gap there instead of duplicating them. On some devices a different font draws these characters, so a word set in that style can show one letter that looks slightly unlike its neighbours.
Small Capital, Turned and Other One-Off Forms
Small capital H is Ę (U+029C). Like most small capitals in Unicode it was encoded for phonetic notation, not as a font feature, which is why small caps text pastes as ordinary characters. Upside-down text uses the turned h, ÉĨ (U+0265). Superscript h is Ę° (U+02B0). Subscript h is â (U+2095). The regional indicator ð is half of a flag: two of them in a row turn into a flag emoji when they spell a country code.
Which H Is Safe to Paste
Bold ð, italic, sans-serif and monospace forms display on nearly every phone and computer. Circled â― and fullwidth ïžĻ are also widely covered. The squared and dark squared forms of H have no emoji version, so they stay black and white. Screen readers may announce a styled H by its full Unicode name or skip it, so keep anything important in plain letters as well.