Silent Sisters

These are Hikaru Chinmoku and Hikari Chinmoku (aka Silent Magician and Silent Paladin from Yu-Gi-Oh). Hikaru (oldest) has always coddled her little sister, always nagging her, especially when Hikari (youngest) started learning swordsmanship and using a real sword. Swinging out of frustration towards her sister's nagging, Hikari accidently cuts Hikaru's neck. Hikaru lives, but loses her voice as a result. Wrecked with guilt, Hikari took a vow of silence so she would, in a way, be in the same boat as her sister. Hikari's never been 100% sure it was true, but Hikaru did eventually forgive her and ease the guilt in Hikari's heart.