Katagiri likes Okada, Ooki is a loner and thinks of Katagiri as her friend and wants to help her get together with Okada who also likes Katagiri but hasn't fully acknowledge his feelings cause boobs keep blocking his thought process.
I wish I would know if the author is having the whole story ready planned or if the things are happening randomly according to the author's mood. I hope for the first because then this already great manga will stay great.