If it's not obvious, Hajime isn't very mentally stable after both his near death experiences in the labyrinth and consuming monsters making jokes transform. Which is why he always prone to bellowing.
When you think about it, it makes perfect sense that Kaori starts out utterly loathing Yui when they meet.
Kaori was incredibly close to Hajime due to their shared interest of Otaku culture and was very close to being in a romantic relationship with him. It's only made worse that Yui used Stockholm Syndrome to romance Hajime, along with the fact Yui practically raped him. Paying in mind Hajime didn't consent to her assault on him in the bath. So Yui stole the sacred milestone of virginity loss together with Hajime from her.
Kaori does calm down after learning she can get the first kiss; which Yui didn't steal.
Kaori was incredibly close to Hajime due to their shared interest of Otaku culture and was very close to being in a romantic relationship with him. It's only made worse that Yui used Stockholm Syndrome to romance Hajime, along with the fact Yui practically raped him. Paying in mind Hajime didn't consent to her assault on him in the bath. So Yui stole the sacred milestone of virginity loss together with Hajime from her.
Kaori does calm down after learning she can get the first kiss; which Yui didn't steal.