i know, it's a little strange. that's why i thought it was possible he just wanted to create an adoring sister.
so the first page would be EITHER:
1)tsukasa has realized that he's been rewriting her diaries, and seeing this, he begins feeling guilty.
2)this is before he started rewriting her diary, and it shows how tsukasa used to act towards him("yuck," cold eyes, impertinent mouth, etc.) and his motivations behind trying to brainwash her. this interpretation seems to make more sense to me, because of the whole "if i reach my hands out..." thing(it would be referring to his plan to brainwash her). and then we jump ahead in time awhile later after his brainwashing and he's scared of what he's created, i guess.
all in all i'd go with #2. 50$ says that the line "that cold body that has stolen my freedom" refers to the fact that he spends all his free time fapping to her(but was still scared when she actually went crazy over him).