I think Kei is his only sister because she also goes to the same school as prez despite not being vocally said to also have a scholarship. It’s possible that Kei moved back with her family to go to the prestigious school too with financial support from her mom. Though, only for the school since she has to help out with the family income like prez. Maybe she couldn’t meet her mother’s expectations and criteria at some point, so was moved back to her dad’s side?
I’m also not too sure until the author clarifies the real reasoning, but that’s my theory on the sister situation.
I was thinking much the same, but wasn't sure if they were going to put a twist in there about a secret sister or something.
So, how many sisters does the president have?
(I guess this could be a spoiler if you haven't read it at all so I'll put a warning here)
*SPOILER*
is it one or two? They haven't fully explained his backstory with his mother leaving yet and I'm still trying to puzzle it out. Because he lives with his dad and sister, but the say his mom left with his sister. Is it the same girl or different?