When introduced, Admiral Ryokugyu has claimed not to have eaten anything in three years. When Ushimaru said “samurai do not get hungry” it would create the possibility of the Admiral Ryokugyu (Green Bull) being a samurai thus allowing the possibility of him being Ushimaru.
If you look at the shadow figure of Green Bull saying he didn’t eat for 3 years, it’s similar to the shadow figure of Ushimaru saying Samurais aren’t hungry, and both of them were shown being happy about it. Lastly, when manga showed Ushimaru’s back clothing, the color of the bull isn’t shown to be green but you can only see it being green in the anime. People who read at the time of manga, would never be able to link the bull being Green with Admiral Green Bull. But now, all gates are open.
Ryokugyu has been called Green Bull, Ushimaru also means bull, and on a recent flashback Ushimaru’s kimono was marked with multiple green bulls.
Coincidence? I think not. I think Oda’s foreshadowing is becoming clearer. Ryokugyu is Zoro’s dad Shimotsuki Ushimaru. He broke out of Kaido’s prison and took on Kaido but was defeated and thrown out of Wano.
Everyone thinks he’s dead, but he survived and was rescued by Marines. He joined them thinking one day he will come back with Marines power and rescue Wano.
Zoro being Ushimaru’s son, while eating from a bowl of noodles, could have foreshadowed Yamato eating from a bowl of rice, who is in the same cave prison as Ushimaru.
What do you think?
*Theory by dr_chopper_451 / gold_D_One_Piece
