No, it is not appropriate. Writing explicit sexual fanfic about characters is unethical and goes against moral and social norms. Such content can also be disrespectful to the original creation and its fans.
Definitely not. Creating such fanfic goes against basic moral principles. Lily James has a career and a public image that she has worked hard to build. Sexual fanfics can be a form of harassment and can cause harm to her reputation and mental well - being.
Love and friendship are common themes. James often shows his deep affection for Lily through his comforting actions. It could be something as simple as a warm smile or a kind word.
One ethical problem is that it can have a negative impact on her career and public perception. People may start to view her in a vulgar way because of this inappropriate fanfic, which is unfair to her as she should be known for her acting skills and professional achievements.
One popular 'james comforts lily fanfic' could be 'The Healing Touch' where James is there for Lily during a difficult time at Hogwarts. He offers her his cloak when she's cold and listens to her problems about her studies.
Family heritage is a common theme. Since they are Potters, many fanfics explore how they deal with the legacy left by their parents and ancestors. Another theme is friendship. They form new friendships at Hogwarts and these relationships are often central to the story.
It could be a story that focuses on the relationship between James and Lily through their portraits. Maybe it shows how their love story is remembered and revered in the wizarding world even after their death.
One possible plot could be that the portraits of James and Lily are somehow damaged or fading, and Harry has to find a way to restore them. He goes on a quest to find ancient spells or magical artifacts that can help.
In some fanfics, James and Lily survive and start to work on a new form of magic that could be used to defeat Voldemort once and for all. They collaborate with the wizarding world's greatest minds, and their survival gives hope to everyone. This changes the mood of the story from one of loss and struggle to one of hope and determination.