A lot of people grew up with family that had harsh expectations of them. He learns to focus more of his time on what he really wants out of life, instead of what he feels is expected of him. Natsumi isn't for everyone, but he is relatable to someone who has gone through that.
And if you said the same about Yoichi, I'd say you hadn't played his route. He has the most character development out of any of the boys, and a lot of faggots eat up le sad backstory.