Perhaps the goddess has the ability to see different timelines. She sees a future where Goku is the most important figure in the universe's survival. So she travels back in time to meet him when he's still young. She becomes his mentor, guiding him not just in power but also in understanding the greater cosmos. As Goku grows up, he starts to see her not just as a mentor but as a love interest, and they develop a relationship that spans different stages of Goku's life.
The goddess could be cursed by an evil force. The only way to break the curse is through a pure hearted mortal's love. Goku, being the pure - hearted Saiyan he is, tries to help her. In the process, he has to go through various trials to understand her true nature. As he does so, he falls in love with her. And through their combined efforts, they break the curse and their relationship blossoms in the wake of victory.
The relationship could start with hostility. Towa might see Goku as a threat to her plans and Goku sees her as an evil force. But then, when they are forced into a situation where they need to rely on each other, like being stranded in a strange realm. They begin to see each other's strengths. For example, Goku might admire Towa's intelligence in dealing with the strange environment, and Towa might be impressed by Goku's unwavering determination.
In the fanfiction, their relationship could be one of mutual admiration. Kid Goku would look up to Future Goku for his experience and power. Future Goku, on the other hand, would be charmed by Kid Goku's innocence and raw potential. They could train together, and during this process, they would form a strong brother - like relationship.
Through shared battles. When they fight side by side against common enemies, they start to trust each other more. For example, in a fight against a group of powerful androids created by a mad scientist, they rely on each other's strengths. Goku uses his martial arts skills and Android 21 uses her technical abilities to analyze the opponents' weaknesses.
Maybe the goddess has a prophecy about Goku being the key to saving her realm from an ancient evil. So she forms a bond with Goku, and as they get to know each other better, Goku starts to develop feelings for her. Their relationship then becomes a driving force for him to fulfill the prophecy and defeat the evil, all while exploring the unique aspects of their two different worlds.
In a Gohan x Goku fanfic, their relationship can be delved into by creating scenarios where they have to rely on each other completely. For example, if they are in a situation where Goku's strength and Gohan's intelligence are both required to escape. Their different personalities can also be highlighted. Goku's carefree nature contrasted with Gohan's more studious and responsible side. And of course, flashbacks to Gohan's childhood and how Goku's presence or absence affected him can add depth to their relationship.
Then, introduce some shared experiences. Maybe they get trapped in a strange dimension together. In this new and dangerous place, they have to rely on each other's strengths. Goku's physical power and Frieza's cunning could be the keys to their survival. As they go through these experiences, they start to see each other in a new light and their relationship begins to change.
They would likely have a very strong bond. Since they are brothers, they would support each other in battles and in their personal growth.
Ichigo can be developed by giving him new powers or abilities related to his connection with the goddess. This could be a way to show his evolution in the fanfiction. The goddess, on the other hand, can be developed by exploring her backstory. Why is she in the human world? What are her goals? By answering these questions, her character becomes more complex and interesting.
You can focus on their emotional bond. For example, show how Goku's pride in Gohan's growth and achievements affects their relationship. It could be about Gohan seeking Goku's approval and Goku being there to give it wholeheartedly.
At first, it might be tense. Bardock is a hardened Saiyan warrior from a different era, and Goku has grown up on Earth with a very different set of values. But as they start to communicate, they would find common ground in their Saiyan blood. Goku's pure - heartedness could gradually win over Bardock, and Bardock's strength and pride could earn Goku's respect.