This character is a Modifier Letter and is mainly used in the Ol Chiki script.
The glyph is not a composition. It has no designated width in East Asian texts. In bidirectional text it is written from left to right. When changing direction it is not mirrored. The word that U+1C7C forms with similar adjacent characters prevents a line break inside it.
The Wikipedia has the following information about this codepoint:
The Ol Chiki (ᱚᱞ ᱪᱤᱠᱤ) script, also known as Ol Chemetʼ (ᱚᱞ ᱪᱮᱢᱮᱫ; ol 'writing', chemetʼ 'learning'), Ol Ciki, Ol, and sometimes as the Santali alphabet is the official writing system for Santali, an Austroasiatic language recognized as an official regional language in India. It was invented by Pandit Raghunath Murmu in 1925, and is one of the official scripts of the Indian Republic. It has 30 letters, the design of which is intended to evoke natural shapes. The script is written from left to right, and has two styles (the print Chapa style and cursive Usara style). Unicode does not maintain a distinction between these two, as is typical for print and cursive variants of a script. In both styles, the script is unicameral (that is, it does not have separate sets of uppercase and lowercase letters).
The shapes of the letters are not arbitrary, but reflect the names for the letters, which are words, usually the names of objects or actions representing conventionalized form in the pictorial shape of the characters.