Daenerys could be a likely character. She has a strong will, and seeing her being hypnotized or using hypnosis on others would be an interesting twist. It could play into her power dynamics, like hypnotizing her dragons to perform different tasks.
Cersei is another one. Given her complex personality and her thirst for power, she might either be a victim of hypnosis or use it herself to further her own goals. Hypnotizing her enemies or those in her court to gain more control over the Seven Kingdoms would be a fascinating plot point.
Theon Greyjoy is also a candidate. His identity and self - worth are often tied to his appearance. A headshave in fanfiction could be a way to explore his further degradation or, conversely, his redemption as he sheds his old self - image and tries to start anew.
Melisandre is a likely candidate. She already has some mysterious powers in the original series, so in fanfiction, it's easy to imagine her delving deeper into mind control. She could use it to sway Stannis Baratheon more effectively or even target his enemies.
The main character is surely Robb Stark in 'robb returns game of thrones fanfic'. Alongside him, his bannermen who were loyal to him before his supposed death would be there. These include men like Greatjon Umber. His enemies from before, like the Boltons, would also be important characters as they would be directly affected by his return. His return might mean vengeance for what they did to him. And his friends and potential allies from other regions, such as some of the Free Folk if the story allows for it, could also be part of the narrative as they might see an opportunity in allying with Robb to change the power balance in Westeros.
Daenerys could be in it. She has a strong personality and is used to being in control. If someone challenges her or her claim to the Iron Throne in the fanfiction, it could lead to a catfight. Also, Margaery. She's clever and manipulative, and a catfight with her could be very interesting as she tries to outwit her opponents using her charm and wits.
Another possibility is Cersei and Jaime. Their relationship is already very complex and twisted. In a fanfiction, it could be a different take on their relationship where Jaime is seen more as a king - like protector to Cersei, and she finds herself in his arms in a more tender and loving way than their usual dynamic in the show.
Theon Greyjoy. He was often in situations where he was bullied and belittled. It's not a stretch to think that some of Ramsay Bolton's men might have given him a wedgie as part of their torture and humiliation tactics.
The king, of course, would be one of the main characters. It could be any of the kings from the 'Game of Thrones' universe, like Joffrey, who was cruel and unpredictable, or perhaps a more noble king like Stannis. The other main character would likely be the person in the king's arms. This could be a new character created for the fanfiction, or it could be an existing character from the show or books, like Sansa who was often at the mercy of different lords and kings.
Obviously Naruto himself. He's the main character of the series so he's bound to be involved. Then there's Sasuke, his rival. They often get into all sorts of situations together, and a drinking game would be no exception. Sakura might also be there, trying to keep Naruto and Sasuke in check while also joining in on the fun.
Arya Stark, Gendry and another character like Edric Storm could be in a love triangle. Arya and Gendry have a history together, but the addition of a third character can create a complex web of relationships. For example, Edric might be a charming nobleman who catches Arya's eye while Gendry is still in the picture, leading to jealousy and difficult choices.
Arya Stark would also be a good choice. Her assassin skills could be put to use in a modern - day context. Maybe she'd be hunting down criminals instead of her enemies in Westeros. And her independent spirit would make her an interesting character to follow as she adapts to the real world.