Rendaku is a phenomenon in Japanese morphophonology that governs the voicing of the initial consonant of a non-initial portion of a compound or prefixed word. Wikipedia

Japanese morphophonology phenomenon in which the initial consonant of a non-initial portion of a compound or prefixed word becomes voiced, e.g. 人 + 人 → 人々 Wikidata

In the Japanese language, a phenomenon which governs the voicing of the initial consonant of the non-initial portion of a compound or prefixed word. An example is 時々 (ときどき, tokidoki), where the second, iterative element "-toki" becomes "-doki" and 折り紙 (おりがみ, origami) where the word 紙 (かみ, kami; paper) becomes "gami". Wiktionary

Sequential voicing in Japanese. Wiktionary (translation)