No, it is not appropriate. Writing fanfic with sexual content often violates ethical and moral standards, especially when it involves fictional characters. It can also make many readers uncomfortable and may not be in line with the original intention of the source material.
There were a few novels that were related to the protagonist's injection of the serum. Among them,"Beauty Man: Starting from the injection of Captain America's serum" was a light novel/derivative Doujinshi novel, and the author was Little Lu Daoyao. In addition,"World Traverser in Marvel" was a light novel written by the master of Sky Swallowing Island, a derivative doujinshi novel. In addition, there was also a book called "A novel injected with super soldier serum", but the specific content and author were not mentioned. Due to the limited search results provided, there might be other related novels, but it was impossible to confirm.
I recommend you to read " Live Broadcast in the Abandoned Village " and " Monster Mother Transformation." " Live Broadcast in the Abandoned Village " was a novel about an urban and entertainment star. The protagonist gained animal abilities after being injected with a drug. " Monster Mother " was about a male protagonist who was unfortunately injected with drugs and turned into a girl. Both novels involved the protagonist being injected with the drug. I hope you like these recommendations!
Satella in the Re:Zero light novel is a very important and enigmatic character. She is central to the themes of the story such as the concept of the Witch. Her existence is linked to the strange and often dangerous events that occur in the world of Re:Zero. Subaru's relationship with her, albeit a complex and often one - sided in a sense, drives much of his character development. The details about her are gradually revealed throughout the course of the light novel, which keeps the readers intrigued about her true nature and purpose.
The theme of self - discovery is also prominent. As Subaru goes through the loops, he learns more about himself, his strengths, and his weaknesses. This is closely related to his interactions with Satella and the other characters. For instance, he discovers that his emotions and relationships play a crucial role in his ability to face challenges. The novel also explores themes of sacrifice and the consequences of one's actions. Subaru often has to make difficult choices that involve sacrificing something or someone in order to achieve a greater good. These choices not only affect him but also the world around him and his relationship with Satella.
Satella's influence on the plot of Re:Zero light novel is multi - faceted. Her connection to Subaru's 'Return by Death' is the most obvious. This ability not only changes the course of individual events but also affects Subaru's relationships with other characters. For example, as he repeatedly comes back to life, he may act differently towards Emilia, Rem, and others, which in turn changes the dynamics of the story. Moreover, the threat of the Witch's Cult associated with Satella looms large over the entire world of Re:Zero. Their actions and Subaru's fight against them form a major part of the plot. Additionally, the mystery of Satella's true nature is a constant thread that runs through the story, leading Subaru to search for answers and driving the plot forward.
When Lao Rongzhi was executed, he would be injected. Although China's law stipulated that the death penalty could be executed by shooting or injection, according to relevant reports and comments, Jiangxi Province, where Lao Rongzhi's case was located, had fully implemented the death penalty by injection. Therefore, Lao Rongzhi was likely to be executed by injection.
There were a few recommended novels about the male protagonist who was injected with the potion. " Live Broadcast in the Abandoned Village " was a novel about an urban and entertainment star. The protagonist gained animal abilities after being injected with a drug. " Monster Mother " was about a male protagonist who was unfortunately injected with drugs and turned into a girl. The male lead of " Mad Soldier Doomsday ", Feng Yi, was also injected with a mutated gene, becoming the strongest Mad Soldier. The male lead of " Almighty Corpse King " had mastered the secret to making potions. These novels all involved the male protagonist being injected with the drug.
You can write about their emotional bond. Maybe Satella has some inner turmoil and Kazuya helps her through it. Use detailed descriptions of their conversations and how they grow closer as friends. Avoid any sexual undertones and keep it clean. You can also explore their backstories and how those affect their present relationship in a positive way.