>>281236406
>But why Shirahoshi?
Its because she makes sense if you add all the little hints Oda gave, by the way Mosa speaks its confirmed she is a girl and that she belongs to the nobility. Its also implied that the Celestial dragons did something bad to Mosa. Mosa also said "that she will need to return to that scary place".
There is also the thing that Mosa means "hairy" and that is how Roger called Shirahoshi. Plus we know that Shirahoshi as a ancestral weapon will be key in the endgame.
No other character fits as well as her as Mosa.