U+30E7 Katakana Letter Small Yo

The Wikipedia has the following information about this codepoint:

The yōon (Japanese: 拗音 (ようおん)), also written as yōon, is a feature of the Japanese language in which a mora is formed with an added [j] sound, i.e., palatalized, or (more rarely in the modern language) with an added [w] sound, i.e. labialized.

Yōon are represented in hiragana using a kana ending in i, such as き (ki) or に (ni), plus a smaller version of one of the three y kana, ya, yu or yo. For example, kyō, "today" (今日), is written きょう [kʲoo], using a small version of the yo kana, よ. Contrast this with kiyō, "skillful" (器用), which is written きよう [kijoo], with a full-sized yo kana. In historical kana orthography, yōon were not distinguished with the smaller kana, and had to be determined by context.

In earlier stages of Japanese, and in certain dialects, yōon can also be formed with the kana wa, wi, we, and wo; for example, くゎ/クヮ kwa,　くゐ/クヰ kwi, くゑ/クヱ kwe,　くを/クヲ kwo. Although obsolete in modern Japanese, kwa and kwi can still be found in several of the Ryukyuan languages today (e.g. Okinawan), while kwe is formed with the digraph くぇ. Kwa also appears in the Kagoshima dialect. Instead of the kana き, these are formed with the kana for ku, く/ク. Some older transliterations in English follow the earlier pronunciation, e.g. Kwaidan, Kwannon, and such yōon may appear in loanwords e.g. ムジカ・アンティクヮ・ケルン "Musica Antiqua Köln". They were also used to write Hakka in Taiwan under Japanese rule.