I think all the readers noticed what O-Tama’s wearing while Luffy giving her piggyback ride. Right?
Oda sensei do this to all the females who join the crew. Let’s start with NAMI
I’m still going to count NICO ROBIN even if she wears it while wearing the cowboy hat
And now with O-TAMA
I know it’s too early to assume things but all One Piece lovers/fans know this: if a character wears Luffy’s hat that character will be his nakama.
Furthermore when Ace visited Wano, Tama formed a bond with and had faith in him. Tama wanted to go out to sea with Ace, but he told her that she was too young at the time. He promised that he would take her with him if she became a kunoichi by the time he returned and Tama waited for him since.
What if Luffy keeps Ace’s promise and takes O-Tama with him?
*Theory by Sero