This is something that needs to happen for several reasons
The SHs will surely help him and Usopp in particular will definitely have a crucial role. But Hajrudin will probably be the one who will fight Dorry and/or Brogy to prevent them from killing Jarul.
To do this, he will surely need a major power up. There are a couple different ways Oda could go about this:
- Dorry and Brogy were put in place as kings of Elbaf by Imu. For Hajrudin to be worthy of the throne, he needs to prove his worth against the puppets Imu is installing
- Dorry and Brogy are the giant warrior pirates. Hajrudin is captain of the new giant warrior pirates. He aims to surpass the old captains.
- Hajrudin was there when Jorul was killed. At the time he was helpless to stop BM. This new scenario gives him an opportunity to stop another tragedy of that magnitude from happening.
- Jarul is the most respected elder in Elbaf. Saving him would allow for him to ascend to the throne, despite being a bastard.
The SHs will surely help him and Usopp in particular will definitely have a crucial role. But Hajrudin will probably be the one who will fight Dorry and/or Brogy to prevent them from killing Jarul.
To do this, he will surely need a major power up. There are a couple different ways Oda could go about this:
- Haki training from Gaban + haki awakening. Oda could reveal Haj already has powerful CoA due to training with Gaban since Dressrosa. The fight with Dorry/Brogy could then awaken CoC.
- A devil fruit. Haj was more than willing to eat a DF to become giant king. It’s why he was in dressrosa to begin with. Options include: the soru soru no mi, a clone of Loki’s fruit, or possibly the grow grow fruit if biblo dies. Oda could also have Hajrudin get buffed from Luffy or Loki’s DFs via some sort of power sharing similar to what Imu can do.
- Buccaneer powers. Wild card here but we know the buccaneers have giant blood. If Hajrudin inherited buccaneer powers through Ida, it would basically discredit the elders’ discrimination against non-elbaf giants.