I will keep it short. This chapter deal with a new character, someone who (I think) will have a lot of impact on Izumi sibling’s life – Izumi Kyouka.
First, from Masamune’s POV, she is treated like a villian. Why? Because she tried to force Sagiri out of her room, which in his opinions is not only wrong, but only backfired horribly. Added with the fact that he (mistakenly) thought that she hated him, and the distance between them keep getting bigger.
However, as we have seen in the story thus far, while Masamune meant well, he didn’t really have a plan to deal with Sagiri’s situation. So in my opinions, he is as guilty as Kyouka is. He keep saying “I want to help Sagiri” but he didn’t actually act on that face, prefer “wait and see” method. It might work, but I don’t think it’s time-effective. It could work after a year OR a decade, he didn’t know. So, I don’t think he got any right to complain about Kyouka’s method.
Next is their conversation. Kyouka said clearly that she didn’t hate Masamune, she hated the fact that he (in her opinion) has to work too early to support Sagiri. Remember, Masamune is her flesh and blood, while Sagiri didn’t. It’s actually understandable that she would priority her own niece above some random girl (which she barely knew)
And lastly, from what I have seen in her reaction toward sibling’s love (and Tsukasa-sensei’s record), I’d bet that there is 50% chance that Izumi Kyouka is also a brocon. It’d be very interesting, don’t you think?