New Epic Seven Side Story - Song of the Sea, Bring Skins System
Karin was busy maintaining order in Reingar amidst an influx of summer visitors when she was suddenly collapsed due to exhaustion. The Phantom CIC sent to Sez, Rin, and Bellona to help Karin.

The next day, Karin and Sez was a fisherman who was overpowered by the waves. This brings together Karin and the Phantom CIC for an unforgettable summer ...
 Song of the Sea, Bring Skins System
Overall I think Skin system very pro F2P right now, Karin skins cost only 1800 skystones (and you can get Karin hero in this event).
Seaside Bellona will be available to players via summons beginning on 8/1. Basically it means re run banner, you not only get skin, but also a hero. I also heard rumor about Sez skin.

Looks like skins doesn't bring stats or skill change, only animation changed.
Epic Seven Skins System

karin e7
 Epic Seven karin summer Skin
Skins can be used on existed heroes.

Full information about update.

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