This character is a Other Letter and is mainly used in the Javanese 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. U+A987 forms an orthographic syllable in Brahmic scripts with similar characters, which prevents a line break inside it.
The Wikipedia has the following information about this codepoint:
Javanese script (natively known as Aksara Jawa, Hanacaraka, Carakan, and Dentawyanjana) is one of Indonesia's traditional scripts developed on the island of Java. The script is primarily used to write the Javanese language, but in the course of its development has also been used to write several other regional languages such as Sundanese and Madurese, the regional lingua franca Malay, as well as the historical languages Kawi and Sanskrit. It heavily influenced the Balinese script from which the system for Sasak developed. Javanese script was actively used by the Javanese people for writing day-to-day and literary texts from at least the mid-16th century CE until the mid-20th century CE, before it was gradually supplanted by the Latin alphabet. Today, the script is taught in the Yogyakarta Special Region as well as the provinces of Central Java and East Java as part of the local curriculum, but with very limited function in everyday use.
Javanese script is an abugida writing system which consists of 20 to 33 basic letters, depending on the language being written. Like other Brahmic scripts, each letter (called an aksara) represents a syllable with the inherent vowel /a/ or /ɔ/ which can be changed with the placement of diacritics around the letter. Each letter has a conjunct form called pasangan, which nullifies the inherent vowel of the previous letter. Traditionally, the script is written without spaces between words (scriptio continua) but is interspersed with a group of decorative punctuation.