Simply knowing his family was attacked and Toki was hurt in the process would’ve sufficed. I think Oda deliberately left this scar on Toki for the purpose of revealing her later on in the story. The upper thigh is a very convenient way for the women of Wano attire to conceal this scar, unlike Nami who wears shorts all the time. Oda wouldn’t randomly give such a scar to a character who is already dead and about to die in the flashback. After all, scars have their importance and backstory in One Piece because many notable characters have distinct scars. Luffy, Zoro, Kaido, Shanks, Whitebeard etc. People have been speculating that the Hiyori we’ve seen so far is actually Toki who jumped 20 years and the real one is being kept hidden. I’m not really sure about that but the reveal of the scar could lead to that being true. This arrow to the leg mark will surely help identify the true identity of Hiyori.
