One possible storyline could be them teaming up for a tournament. Gohan's martial arts skills combined with 18's strength would make for an interesting duo in the fighting arena. They could face various opponents and learn to trust each other's abilities more.
A possible plot is that Android 21, who has some glitches in her system related to her emotions, is healed by Gohan's kindness. As a result, she starts to develop feelings for him. They then have to deal with the fact that their relationship is not accepted by some in the Z - Fighter community because of Android 21's origin. This leads to a story full of drama and self - discovery for both of them.
One interesting storyline could be about Naruto having a different power origin. For example, instead of being the host of the Nine - Tails, he might gain his power from an ancient sage. This could change the whole dynamic of his character development and relationships in the story.
Maybe in the fanfiction, Android 18 gets injured while protecting Gohan from a new powerful enemy. Gohan then takes care of her and in that time of vulnerability, they realize their feelings for each other. This could lead to them exploring a relationship while also trying to figure out how to defeat the enemy that still lurks.
One possible storyline could be Goku taking Baby Gohan on a special training adventure in a new and mysterious realm. They could encounter strange creatures and learn new techniques together.
One possible storyline could be that Gohan and Black Widow are brought together by some sort of multiverse accident. They find themselves in a strange new world and have to rely on each other's skills. Gohan's superhuman strength and Black Widow's espionage expertise would make for an exciting combination as they face various threats.