U+309A Combining Katakana-Hiragana Semi-Voiced Sound Mark

The Wikipedia has the following information about this codepoint:

The dakuten (Japanese: 濁点, Japanese pronunciation: [dakɯ̥teꜜɴ] or [dakɯ̥teɴ], lit. "voicing mark"), colloquially ten-ten (点々, "dots"), is a diacritic most often used in the Japanese kana syllabaries to indicate that the consonant of a syllable should be pronounced voiced, for instance, on sounds that have undergone rendaku (sequential voicing).

The handakuten (半濁点, Japanese pronunciation: [handaꜜkɯ̥teɴ], lit. "half voicing mark"), colloquially maru (丸, "circle"), is a diacritic used with the kana for syllables starting with h to indicate that they should instead be pronounced with [p].