I felt a deeper idea going on in Onimai.
In Onimai's story the brother hides himself from society due to the weight and stress of being the big brother. He becomes a neet and hasn't seen the outside world in 2 years.
So the sister concocted a plan to use her smarts to make a drug that turns him into a young middle school girl free from the weight of those responsibilities because he’s the younger sibling now. Her sister takes the opportunity to re introduce him to society once again with different mindset.
His now big sister gives him the emotional comfort and support to take one step at a time seeing the beauty in the world.
I feel like I can relate to the feeling
I have very little emotional connection with the people around me, I don't want to show weakness to people around as I mostly get back the response “you'll be fine” or “stop whining”.
I'm a man and I got to be tough but I can see the fantasy of not having to cover it.
I'm definitely projecting but whatever