For Art's Sake is the eighth webisode of the third season.
The webisode starts in the art room with Katana busy painting. June Moone enters the room, wondering why Katana was still in the art room, as all the other students had packed up and headed out already, asking Katana whether she was ready to go. Katana then says she's almost ready, explaining that she wanted her artistic debut to be perfect.
In the Super Hero High foyer, Amanda Waller is welcoming the visitors to the Super Hero High Student Art fundraiser, giving a special welcome to Silver St. Cloud and explaining that she'd generously given a piece from her gallery, before asking Supergirl to lift off the sheet covering the painting. Supergirl then lifts the sheet off, only to discover the painting was gone, as Silver expresses her worry. Just then one of the Double Dare twins swings across to higher level of the foyer, with the painting in hand. She calls the event a great fundraiser as she folds the painting, stuffing it in her rucksack, with the other twin exclaiming that all the proceeds went to the Double Dare Twins. Supergirl angrily tells them to give the painting back, as she flies towards the Twins. However one of the twins then takes out a chunk of kryptonite and then throwing it at Supergirl. In response Supergirl collapses, before Amanda quickly picks up the kryptonite, throwing it away. Amanda then calls for someone to stop them as she tends to Supergirl.
Katana then arrives on the scene, quickly jumping onto a curtain and beginning to climb up to where the twins had just ran to. One of the twins then takes out a knife and cuts the curtain, causing Katana to fall. Katana quickly manages to stab her sword into the wall, using it to vault up to the twins. The twins then fall back on plan D, falling back and using Katana's sword to swing into the central corridor, before activating the emergency door, in an attempt to block off Katana. However Katana uses one of the nearby curtains to skilfully slide under it before it close, with Supergirl trying to do the same, but to no avail.
One of the twins then claims that they got to love super-proof steel, before the two run off, heading into the art room. Katana chases after them, telling them to stop as she reaches the classroom. The twins then take Katana's artwork, holding Katana's sword up to it, in an attempt to deter Katana away. Katana demands they put it down, but the twins only dare her.
Katana accepts the dare and tosses a multitude of paint-brushes at the twins, pinning one to the wall, with the other twin cheekily saying she missed her. However Katana keeps throwing and manages to pin her too. Katana then begins to squirt some paint-tubes at the twins, accidently hitting her painting, just as the twins try to split. Katana then slides a paint-pallet on the floor, causing the fleeing twin to trip and knock right into the other. Katana then takes the painting they'd stolen back, just as Silver arrives calling Katana's work a masterpiece. Katana believes she's referring to the stolen painting, saying that's why the twins wanted to steal it, only to realize Silver's talking about her art, with Silver asking Katana where she found her inspiration. Katana then reveals she believed it had found her.