edit: see the 4th reply for the debunking
The image of the kiriko skin is in the exact format of a shop card for the Premium battlepass. In the past 2 seasons there have been two of these cards in the seasonal section of the shop, one for a normal battlepass and one for a level-boosted battlepass. You can tell this isn’t the level boosted card because that has “+20” on it and is much wider.
Notably, in the past 2 seasons, the normal card has featured a Legendary skin (Posiedon Rammatra, Hinotori Kiriko) and the boosted card featured the Mythic skin. If this pattern continues, then the Kiriko skin isn’t mythic
Now of course this pattern has only happened for two seasons and I think this skin is on the upper end of quality for a legendary, so there’s definitely still a chance this is mythic.