It could lead to a completely different character dynamic and story arc. Maybe she'd face different challenges and have a unique perspective on being a hero.
As someone who loves reading novels, I can't provide a dynamic picture. But if you need any other information about Girls 'Generation, I can try my best to answer your questions.
The following were some novel recommendations similar to "The Forever Girl":"Book of Troubled Times"(Author: Ji Cha),"Spiritual Walker"(Author: Xiao Langjun),"Tang's Table"(Author: Jie Yu 24),"King of Familiar"(Author: Qingquan Liuxiang),"Fairy, Please Listen to My Explanation", etc. These novels might have similar plots or theme to The Forever Girl.
Well, one possible plot could be that Deku accidentally drinks a strange potion created by a villain. This potion has the side - effect of changing his gender to female. At first, he's shocked and confused. But then, he realizes that he can use this new form to his advantage in hero work. For example, he might be able to infiltrate a female - only villain group more easily. He also has to deal with his friends' reactions, some are surprised while others are supportive and help him adjust to his new body while still being a hero.
I'm not entirely sure as there could be various interpretations. It might be about a love that endures through time. Maybe it's a story of a man who realizes that a particular woman is meant to be his forever.