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+0448 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:
Sha or Shu, alternatively transliterated Ša (Ш ш; italics: Ш ш) is a letter of the Glagolitic and Cyrillic scripts. It commonly represents the voiceless postalveolar fricative /ʃ/. More precisely, the sound in Russian denoted by ш is commonly transcribed as a palatoalveolar fricative but is actually a voiceless retroflex fricative /ʂ/. It is used in every variation of the Cyrillic alphabet for Slavic and non-Slavic languages.
In English, Sha is romanized as sh or as š, the latter being the equivalent letter in the Latin alphabets of Czech, Slovak, Slovene, Serbo-Croatian, Macedonian, Latvian and Lithuanian.