I like this better than the main story. In here, Soutarou's feelings are described more and it's nice to finally understand what he's thinking beneath that "good younger brother" facade. this story isn't romance that centered on the smut, but rather, it's centered in how Soutarou's feelings changes from time to time. The smut only appears starting from chapter 13, which is half of the novel. And the smut is only 30% (max) of the story. however, his "pov" end up sooner than the one in the main story. So here, it's not going to describe what happened in chapter 22 of lean tuna in Soutarou's pov. The same when Amane ask Soutarou to help her in chapter 4 (I think) in the lean tuna, it's not described how Soutarou thinks and skipped it right to the decision at the end of the chapter.