The glyph is not a composition. Its width in East Asian texts is determined by its context. It can be displayed wide or narrow. In bidirectional text it is written from left to right. When changing direction it is not mirrored. The word that U+0437 forms with similar adjacent characters prevents a line break inside it. The glyph can be confused with one other glyph.
The Wikipedia has the following information about this codepoint:
Ze (З з; italics: Зз) is a letter of the Cyrillic script.
It commonly represents the voiced alveolar fricative /z/, like the pronunciation of ⟨z⟩ in "zebra".
Ze is romanized using the Latin letter ⟨z⟩.
The shape of Ze is very similar to the Arabic numeral three ⟨3⟩, and should not be confused with the Cyrillic letter E ⟨Э⟩.