Variation Selector-1

It only tells a renderer which approved shape to draw next. It has no standalone reading: the base-plus-selector pair carries the instruction.

The documented trail for this character begins in standards work, not as a manuscript mark. Unicode 3.2's 2002 specification introduced variation selectors for plain text that needed a particular glyph while keeping the same underlying character, including cases from CJK and Mongolian writing.

VS1's defined uses later span CJK compatibility forms, mathematical shapes such as a serifed union, and reversed-shaping forms in Phags-pa. The pair—not VS1 alone—decides the result.

Why is it invisible?

Invisible is the expected result. The selector is zero-width and default-ignorable.

It must immediately follow a defined base. After an unrelated character, or when the pair is unsupported, the base keeps its ordinary glyph and VS1 disappears; it is not a general styling switch.

Mongolian uses script-specific free selectors, while registered ideographic variation sequences use supplementary selectors; those related systems are not interchangeable with VS1.