This character is a Other Letter and is mainly used in the Katakana script.
The glyph is not a composition. Its East Asian Width is wide. In bidirectional text it is written from left to right. When changing direction it is not mirrored. This katakana joins with other adjacent katakana to form a word. U+30A4 offers a line break opportunity at its position, except in some numeric contexts. The glyph can be confused with one other glyph.
The Wikipedia has the following information about this codepoint:
I (い in hiragana or イ in katakana) is one of the Japanese kana each of which represents one mora. い is based on the sōsho style of the kanji character 以, and イ is from the radical (left part) of the kanji character 伊. In the modern Japanese system of sound order, it occupies the second position of the syllable chart, between あ and う. Additionally, it is the first letter in Iroha, before ろ. Both represent the sound [i]. In the Ainu language, katakana イ is written as y in their Latin-based syllable chart, and a small ィ after another katakana represents a diphthong.