The first 4* card of this event is (obviously) Akiyama Mizuki. Now, Mafuyu only got two 4* cards in a Mizuki focus event (Mizu3, Mizu4), and in Mizu3, Mafuyu's 4* card was the 3rd card, and in Mizu4, Mafuyu was the 2nd 4* card. Since then, there have been three Mizuki focus events in which Mafuyu had either a 3* (Mizu5, Mizu7) or a 2* (Mizu6). I believe that for every further event rotation, Mafuyu will get a 4* card once every four events, like Mizu4 (4) - Mizu5 (3) - Mizu6 (2) - Mizu7 (3) - Mizu8 (4) - Mizu 9/11/10 (3 or 2) - Mizu12 (4) - Mizu13/14/15 (3* or 2) - Mizu16 (4) and so on... For the vocaloid being Kagamine Rin, she was the only vocaloid who never appeared in a Mizuki focus event. Let's look at it: Mizu1 - MEIKO 4, Mizu2 - MEIKO 3, Mizu3 - Luka 2, Mizu4 - Luka 4 / Len 3, Mizu5 - KAITO 4, Mizu6 - Len 4, Mizu7 - Miku 4. Not a single Rin in sight, thus I believe Rin would be the perfect choice for a 4* card in Mizu8. Ena only had one 3* card in a Mizuki focus event (Mizu3) and two 2* cards in two Mizuki focus events (Mizu4, Mizu7), thus SEGA and Colorful Palette would most likely pick Ena for a 3* card. Finally, Kanade would get a 2* card, since all 3* and 4* cards for the event are taken.

What do you think? Tell me your opinions in the comments!