Fullwidth Latin Small Letter J

It gives lowercase Latin j a full-cell width.

Zenkaku means full-width. Since the letterpress era, Japanese typesetting placed fixed-width Latin letters upright beside kana (Japanese syllabic characters) and kanji (Chinese-origin characters used in Japanese). Computer text kept separate widths so conversions of older East Asian text could preserve the distinction.

Japanese layout guidance favors fullwidth Latin in vertical text and generally discourages it in horizontal prose for appearance.