Action Girl: Even without transforming, Touka briefly demonstrated considerable martial arts skills when she ambushed Takatora.
Combat Tentacles: Subverted. Idun is shown to be able to manipulate Helheim vines just like the Overlords, but she never uses them in battle.
Death Seeker: When Touka is defeated by Takatora, she seems to be egging him on to kill her, saying that she would return and try to kill him again if he spares her. He can't bring himself to do it, but Ryōma, on the other hand
Evil Cannot Comprehend Good: Touka doesn't understand that Takatora spared her because of his bond with her. Ryoma on the other hand is more willing to do so. However, it's partially averted in that she recognizes that Takatora was a good person despite everything else.
Expy: Idun's Ringo Arms is basically a copy of Mars' Golden Arms, using the same fruit and armaments.
Its design is slightly more reminiscent of Kamuro's Silver Arms, while Kaito's version of Ringo Arms resembles Mars more.
Good Counterpart: Touka to Ryoma. Both come from the same facility, which explains how both are screwed up. But while the experimentation removed anything human in Ryoma, Touka's revenge, however extreme and misguided, is aimed at paying Yggdrasil back for their inhumanity, and she is still genuinely fond of Takatora, cherishing their childhood together.
Green Thumb: Touka can control Helheim flora much like an Overlord.
Sadist: The expression on Touka's face when recounting her murder of Amagi Kureshima shows that she thoroughly enjoyed getting her revenge. That she chooses to target everyone connected to him, not just the man himself, calls into question just how much of her motives are rooted in revenge.
Thinking Up Portals: Idunn's Lockseed gives her the power to open and manipulate Cracks to and from Helheim, which she uses to make quick escapes and get the drop on her targets.
Tragic Monster: While Touka does want to bring Yggdrasill and the Kureshimas down, she does genuinely cherish her time with Takatora and in her dying moments, thinks back to said moments and laments that someone like Takatora had to be of the Kureshima family and Yggdrasill.
Unwitting Pawn: In a similar way to Tyrant mentioned below, Tōka ended up serving as a test subject for one of Ryōma's experimental prototype lockseeds. In her case, her successful use of the Forbidden Ringo Lockseed's powers helped him prove that the Golden Fruit does indeed exist.