There were a few novels that could be recommended, including Those Years Living in the Future World of Dragon Ball, If Dragon Ball, Latiz took Gohan away, and The Strongest Sun Gohan of Dragon Ball. These novels all used Gohan as the protagonist, telling his growth and adventures in the Dragon Ball world. These novels might satisfy your need for Gohan to be the protagonist.
In this fanfiction, Gohan might learn valuable life lessons from Grandpa Gohan. Maybe Grandpa Gohan would teach Gohan some old - fashioned martial arts techniques that have been forgotten over time.
In such a fanfiction, perhaps future Gohan could warn present - day Gohan about upcoming threats that he has faced in his own timeline. He might share his experiences and knowledge, which could make present Gohan a stronger fighter and a wiser person.
Piccolo might also be a savior. He has a soft spot for Gohan since they trained together. He could use his strategic mind and powerful attacks to outwit Raditz and rescue Gohan. Maybe he teams up with Goku for an even more epic rescue mission.
I recommend two novels to you: " Stealing the Dragon Prince's Only Pearl " and " Online Games Dragon Return to the Shallow Abyss." " Stealing the Dragon Prince's Only Orb " told the story of a human stealing the Dragon Prince's Divine Power Orb, causing the Dragon Prince to degenerate into a small dragon, and the human being was hunted down by the Sea Tribe. The main character of " The Dragon of Online Games Return to the Shallow Abyss " was the young master. After stealing the dragon egg, he was chased by the divine dragon and was forced to embark on an adventure. Both novels fit the plot you described where the protagonist stole the dragon core.
Fan Xian successfully obtained the key by breaking into the empress dowager's bedroom at night and stealing the key. He used the key to open the box left by Ye Qingmei and found a sniper rifle and two letters inside. Fan Xian had chosen to barge into the empress dowager's chambers at night because he knew the key was in the empress dowager's hands. Fan Xian did not return the key. Instead, he made a fake key and put it back in its original place to avoid arousing the empress dowager's suspicion. Thus, Fan Xian successfully stole the key.