the handakuten — the small circle diacritic (゜) used with kana to change an 'h' sound into a 'p' sound.
「は」に半濁点をつけると「ぱ」になる。
Attach a handakuten to は and it becomes ぱ.
半濁点（゜）は主にパ行の音を表すために使われる。
The handakuten (゜) is mainly used to represent the 'pa' row sounds.
手書きでは半濁点を小さな丸で書くが、見落とされないよう注意が必要だ。
When handwriting, the handakuten is drawn as a small circle, but you need to be careful not to miss it.