There are many reasons to believe hibari is akainu's daugher aside from their speech.
1. The rose Akainu has on his suit is a japanese variant of a rose called Hibari
2. She is a member of Sword, which Akainu has a tattoo off
3. There is an old spin-off manga of one piece based on a school, here Hibari was first introduced and she has a crush on the Koby of this world
4. In that Spin-off Akainu is the principal of the school, and he is the father of this girl who happens to be in love with Koby and share her name in this world
 
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