A 'Harvest Moon' pregnant fanfic can add depth to the existing game world. In the game, family and relationships are important aspects. A pregnancy can bring about new challenges and growth for the characters. For instance, if it's a female character, she might have to balance her usual tasks like taking care of the farm and animals with her pregnancy. Fanfic writers can explore the emotional journey of the character during this time, from the initial shock to the anticipation of motherhood.
I think it depends on the specific story. Some Harvest Moon fanfics might introduce the idea of fairies in a magical or fantasy context, and it can be quite believable within that fictional world.
You can start by looking on fanfic - specific websites like Archive of Our Own (AO3). There are often many 'Harvest Moon' fanfics there, and you can filter for ones related to pregnancy. Another option is FanFiction.net, which has a large collection as well. Just search for 'Harvest Moon' and then narrow it down to the pregnancy - themed ones.
No, they're not the same. Story of Seasons is a new series that developed from the Harvest Moon franchise but has some distinct features and gameplay differences.
They aren't identical. Harvest Moon was the original, and Story of Seasons is a continuation with its own tweaks and improvements. The worlds, quests, and overall feel can vary between the two.