How They Meet, How They Come Together, and How Their Relationship Develops
Gohan and Loki meet as teens, either between training for the Cell games or after the Cell games. Either Gohan helps her with something, they end up on an adventure, or both. Loki keeps an eye on him because he caught her interest. She also gives Gohan a way to stay in contact. They talk occasionally over the years/centuries depending on time in Asgard. They meet again in person as adults after Gohan's divorce. She finds him in the park grading papers (Split series). Loki teases Gohan. Gohan is shy and awkward at first, but gets sassy over time. They have meaningful conversations, and their friendship develops. They grow to trust each other and respect each other. They also give each other support and suggestions about problems they have in their lives. There is also respect, equality, independence, and comfort around each other. Over time, their feelings grow. They learn how to work with each other and become a team. They start dating at some point, and they end up complementing each other.
During a trial on Asgard, Loki mentions that she was spending time with Gohan when forced to tell the truth (Stevie Rogers and Dick Grayson: An interdimensional Love story). Someone accidentally marries them (probably either Goku or Thor). The ceremony is permanent (literally til death do us part). This could happen either before or after Loki's trial.
They also have some adventures, including one where they need to save Gohan's friends and family.
Below are some possible plot differences for Dragon Ball Z.
For some Cell games plot differences: (a) instead of deciding not to return after dying, he is required to stay for seven years before returning, (b) Goku keeps fighting Cell, and at a point in the fight after the stage is destroyed, Gohan jumps in the fight angry about his dad nearly getting killed, and defeats Cell.
When Gohan starts High School, he doesn't remember Hercule. Once they explain who he is and Gohan remembers him, Gohan starts laughing uncontrollably and Videl gets angry (not knowing that laughter was really a good reaction considering (There are also two Videl/Gohan fanfics on fanfiction.net that have these two concepts.)
Both Saiyanman and the Buu Saga can be optional or changed.