I can't really point to one specific fanfiction as there are so many out there. But you can start by looking at popular fanfiction websites and filtering for Dragon Ball Z, Krillin, and Android 18. Check the reviews and ratings to find a good one.
In some fanfictions, the focus might be on how Android 18's android nature affects their relationship. For instance, there could be a story where Krillin has to deal with Android 18 having a malfunction that makes her act differently. He then has to find a way to fix her without losing the essence of who she is, and this creates a lot of emotional and action - filled moments in the fanfiction.
Yes, there are. For example, some fanfictions might explore Krillin's character in new and unique ways, like giving him new powers or putting him in different situations within the Dragon Ball universe.
There are no such inappropriate 'Straight Shota' stories in the official Dragon Ball Z canon. Dragon Ball Z mainly focuses on epic battles, power-ups, and the adventures of Goku and his friends to protect the Earth from various villains.
Dragon Ball Z is both anime and manga. The anime was adapted from the manga and they share the same story and characters, but presented in different mediums.
One alternative is to focus on character backstories. You could write about the early days of Piccolo, how he came to be the way he is. Another option is to do crossovers with other non - sexual universes. Maybe a story where the Dragon Ball Z characters meet characters from a magical anime world and they have to work together to solve a problem. Also, you can write about the relationships between the characters in a platonic way, like the deepening of the friendship between Gohan and Krillin.
A Kryptonian in the Dragon Ball Z universe could potentially be a very powerful addition. Their natural abilities like super strength, flight, and heat vision could make them a force to be reckoned with. However, they would also face challenges as the Dragon Ball Z world has its own power scale with ki-based powers. They might have to adapt to the different fighting styles and power sources. Maybe they could learn to use ki in addition to their Kryptonian powers, or they could find a way to combine the two in unique ways.