It was all Misha's doing! She was jealous that Hisao gave the cat to Shizune, so she turned back time to give herself another chance. Only this time Hisao ended up with Emi, so she had to redo it once more. When he ended up with Kenji the sixth time around she was freakin' mad at Hisao and locked him in the loop permanently to get her revenge on him.
What she didn't plan on was Hisao and the other girls finally breaking free from the rails she set them and now can use the time loop freely. By doing that they messed up whatever Misha spell Misha cast, and now she's locked in the loop along with everyone else.
The reason Misha and Shizune are avoiding the others is so she doesn't slip up and give hersalf away accidentally. Oh, and Shizune is controlled by Misha, obviously.
There are only two ways of finally breaking the loop: Either kill Misha or for Hisao to take her back with him after the fireworks.
Note:
While I asked For Leo's permission to post my ramblings here, he refused to confirm or deny their veracity. So we won't know for sure until the sequel
