This is just an assumption but the text in that page with Shachi says “読ん・・・” which is a part of ‘read’.
So I guess it did seem like Shachi had an advantage and was about to say “can read you like a book” or something along those lines but Arima… did that thing he always does.
Rize and Shachi are living together. They both have a conversation on the veranda.
Rize: So Shachi was the one who killed my teacher/mentor? Shachi: He died on his own. Can’t win against the aged. (i’m not sure if it’s this or ‘can’t win against aging’)
Rize: Hmm~…
Rize hugs Shachi’s arm.
Rize: Hey, so that means Shachi is my dad?
(instead of ‘you’, Rize refers to him as ‘Shachi’)
he refers to her as his bitch daughter a few times…. but he cares
Also Rize and Shachi have the same coloring on their kagune (at least in he anime, which was made with Ishida’s influence to a degree, so I wonder if that plays into Rize’s uniqueness)