Yes, it can be appropriate. If both the wife and the husband have an open and healthy attitude towards sex, sharing sex stories can be a way to add some spice to their relationship. It can also be a means of understanding each other's sexual desires better.
In no way can this be considered right. Such a scenario in erotic stories or in real life violates basic principles of family relationships, respect, and human decency. It is a very disturbing and inappropriate concept.
This is completely unethical in any context. Incestuous relationships are not acceptable in society and violate basic moral and ethical norms. It is important to uphold healthy family boundaries and proper values.
We should focus on positive, healthy and family - friendly literature, such as classic novels like 'Pride and Prejudice' which offers great stories about love, society and human nature in a proper way.
The main problem is that it's inappropriate. Pokemon is a family - friendly franchise, and this type of fanfiction goes against its wholesome image. It also violates ethical boundaries as it involves sexual content related to something that is meant for a general and often young audience.
She could start by choosing stories that are in line with their shared interests. For example, if they both love adventure, find sex stories set in an adventurous context like a passionate encounter during a jungle exploration. Another way is to set the mood. Dim the lights, play some soft music, and then start reading the story in a seductive voice.