U+31F1 Katakana Letter Small Si

The Wikipedia has the following information about this codepoint:

し, in hiragana, or シ in katakana, is one of the Japanese kana, which each represent one mora. Both represent the phonemes /si/, reflected in the Nihon-shiki and Kunrei-shiki romanization si, although for phonological reasons, the actual pronunciation is [ɕi] , which is reflected in the Hepburn romanization shi. The shapes of these kana have origins in the character 之. The katakana form has become increasingly popular as an emoticon in the Western world due to its resemblance to a smiling face.

This character may be combined with a dakuten, forming じ in hiragana, ジ in katakana, and ji in Hepburn romanization; the pronunciation becomes /zi/ (phonetically [d͡ʑi] or [ʑi] in the middle of words).

The dakuten form of this character is used when transliterating "di" occasionally, as opposed to チ's dakuten form, or a de assigned to a small i; for example, Aladdin is written as アラジン Arajin, and radio is written as ラジオ.

In the Ainu language, シ is used to represent the ʃi sound. It can also be written as a small ㇱ to represent a final s sound, pronounced ɕ.