Upgrade cost should depend on the order you obtained the girls in, but it seems to be bugged. Your Ankyo appears to be your #13 girl, which is obviously impossible since she's supposed to be around 5th. For me she is 9th, after several girls including Fairy (!), and costs 8.7M to upgrade. Since upgrade price so drastically depends on the order, maybe they should look into fixing it before releasing more affection scenes? Or you will have to pay 60 million if the next girl somehow ends up being near the end of your list.

Here's the table, btw: http://harem-battle.club/wiki/Harem-Heroes/HH:Harem (under "Costs from your first haremette to your 75th")

I got both red battler affections for free (not including the upgrade cost) btw, but for Ankyo I only got 4 stars for some reason.