@Anya:
Harata lol. Was that on purpose?
@Kanon: As for Michiru, I guess I can share the small bits here because they will not be animated. It was just shown a bit at the beginning of this season (episode 1), but there is more.
In the school trip, Michiru taking Chihaya's phone's battery and even yelling at her while tearing up for not enjoying the trip might seem excessive/ overreaction to those who don't know how close these two actually are. She even specifically chose the locations so Chihaya would enjoy the trip.
This is how it all re-started: Chihaya in middle school became very lonely after Arata moved back to Fukui and Taichi went to another high profile school. At the start of her middle school, her loneliness was compounded by how she was kind of avoided by everyone in her class, especially the girls, because of her obsession with karuta. It was understandable when the girls were interested in girl-talk or accessories, Chihaya always wanted to discuss about karuta - a not very interesting topic for the girls her age (or anyone in general, to put it bluntly).
In the end, she didn't have anyone to talk with. At that time, the only one who approached her on her own and stayed by her side during that entire time was Michiru. Chihaya also got a place of her own in the track and field team thanks to Michiru. And little by little, she got used to her classmates and made more friends. Michiru is also her first friend who visited her house to play with her. Although Michiru never got into karuta in the end, she respected Chihaya's passion for karuta which healed Chihaya little by little. Michiru was basically the person who filled the void in Chihaya left by the departures of Arata and Taichi from her life. That's how much important Michiru's existence has been in Chihaya's life.
Little backstories always help. But we cannot cover everything I guess.