Hatsune before meeting Sakiko was basically just a blank slate. It's like Sakiko painted something small yet beautiful on her and from there she started sloppily splotching paint on the rest of the canvas to "finish" the job
The way Hatsune worded this is screwing me up so bad
It's "I have to be someone Saki-chan knows."
But when translated more directly...
I have to be a human Saki-chan knows...
I have to be a human [for Saki-chan]...
Hatsune before meeting Sakiko was basically just a blank slate. It's like Sakiko painted something small yet beautiful on her and from there she started sloppily splotching paint on the rest of the canvas to "finish" the job