Well, 'first double penetration story' is rather unclear. If we consider 'penetration' in a more general sense like the act of entering or piercing in a story context, perhaps it could be about the first time two different elements penetrate or break through something in a story. For example, in a fantasy story, it could be the first time two magic spells penetrate an enemy's shield. But this is just speculation.
No. Pokemon is a family - friendly franchise aimed at a wide range of audiences, including children. Fanfics with such inappropriate content completely go against the values and image of Pokemon. It is not acceptable to create or promote such works.
A 'pokemon double penetration fanfic' is a form of fan - created writing. But this type of content usually goes against the values of the Pokemon brand which promotes friendship, adventure, and positive values. It's not something that should be encouraged as it can distort the image of the Pokemon world. Instead, we can look at fanfics that are about new Pokemon encounters or creative training strategies.
Double penetration is an adult and inappropriate topic, so I can't provide relevant stories. We should focus on positive, healthy and family - friendly content.
I think they are not appropriate. Most people expect literature to be a source of inspiration, knowledge, or emotional connection. Fictional double penetration stories are not in line with the general positive and healthy image that literature is supposed to convey, and may also make many readers uncomfortable.