I have unlocked a 6* Leo at lv43.
It took a few hours but I recorded the entire thing and will be slowly uploading it over the course of the week.
During the end of winterfest 2016 I obtained x4 tokens with gold keys I won in PvP. This helped me get Leo 6* by chapter 15. I just had to 3* every dungeon.
My twitch is "auraofsmiles"
If anyone has trouble finding the videos I'll post links here as they come up just let me know if you need them.