Poor Chihiro. Ayumi has every right to be emotionally confused, but Chihiro has that same right, and she is at least trying to reach out to her friend. Ayumi is only making things worse for herself and for Chihiro by refusing to answer the phone.
Lune is on the move a little earlier than expected. She was always going to interfere in some capacity, but taking action here, before Keima sorts himself out, maximizes the tension of this situation. It also helps to emphasize just how difficult the conquest of Ayumi is.

Why can't she move five spaces down?
Sumire makes a very nice cameo here. One of the biggest strengths of this series is its use of dramatic irony thanks to the conquest system. Having each girl lose their memory of the conquest allows for reappearances like this one with Sumire, where the girl’s interaction with Keima means more to the audience, thanks to our memory of her conquest, than to the girl herself. This also provides the indirect benefit of allowing the audience to better identify with Keima through the connection of those shared memories.
Keima does ultimately have his priorities straight in focusing on saving the world, but he could stand to be even slightly considerate of Chihiro’s feelings. Asking her to team up with him to win over Ayumi is hurtful enough, but dismissing her feelings as “petty issues” is awful of him. He doesn’t seem to be deliberately antagonizing her for some greater reason, so his treatment of Chihiro is just unnecessary cruelty.

Keima decapitated; series over
To make matters even worse for Chihiro, Ayumi doesn’t just announce her intention to quit the band, but she says she “can’t be in the band with you anymore.” Whether that “you” is plural or specific to Chihiro is unclear, but either way, this is another major blow to the already-suffering Chihiro. The last few chapters have established Ayumi as a sympathetic figure, but she hasn’t been through nearly as much as Chihiro, if only because Ayumi is at least in control of her own situation. Chihiro can only react to all these terrible things happening to her.
Lune’s decision to target everyone is unexpected but brilliant. Involving so many more girls than Keima could possibly account for will make this upcoming climax even better than it already promises to be.
Final Flash: Whenever this climax finally happens, it has quite a lot of fantastic buildup to live up to.