Well, it's not really acceptable. The Undertale community is supposed to be inclusive but also appropriate. Fan fiction should focus more on the positive aspects of the game, like the story, the characters' development, and the unique world it presents. NSFW content, especially with a sexual orientation focus like 'gay' in this case, can make a lot of fans uncomfortable and may even violate community guidelines in many platforms.
Pornographic stories are not the kind of content that should be promoted as 'famous'. We should stay away from porn and instead look at positive gay - related works like the movie 'Moonlight' which tells a poignant and profound story of a young black gay man growing up.
One common theme is probably the exploration of relationships between male characters in the Undertale world. It could be about how they support each other and grow closer.
Love and acceptance are common themes. Just like in any relationship story, in gay Undertale stories, the characters often have to face the challenge of being accepted by their friends, family (if applicable in the Undertale context), and the community around them. They also deal with self - acceptance, realizing and coming to terms with their own sexual orientation within the framework of the Undertale world.
The fandom can enforce strict community guidelines on the platforms where fan works are shared. Moderators can actively look for and remove any NSFW content, including those with a 'gay undertale' theme. Also, fans can report such inappropriate works when they come across them.
I'm not really into specific 'undertale gay fanfic' recommendations. However, you can try searching on fanfic platforms like Archive of Our Own. There are often a lot of fanfics in different categories including gay-themed ones related to Undertale.
In a gay Undertale story, perhaps a pair of male characters from different areas of the Underground meet by chance. They have to overcome their initial differences and prejudices. As they get to know each other better, they develop a strong emotional connection that turns into a romantic relationship, all while dealing with the unique magic and social structure of the Undertale universe.
Sharing or promoting pornographic stories is unethical and not suitable content. We should focus on positive, healthy and inclusive LGBT - related stories that are family - friendly, such as coming - out stories that inspire understanding and acceptance.