Well, Naruto is a likely candidate as he is constantly evolving and taking on challenges that seem impossible. His determination could lead him to the 'Gate of Death'. Then there's Gaara. His journey from being a feared outcast to a protector could potentially involve him facing the 'Gate of Death' in some fanfictions. And Madara Uchiha, being one of the most powerful and complex characters, might also be connected to this concept. Maybe in some alternate storylines where he attempts to reach an even greater power level through something like the 'Gate of Death'.
Naruto himself could be associated with it. Given his propensity for pushing his limits, he might be the one to discover or be forced into the situation related to the 'Gate of Death'. Another could be Sasuke. His quest for power might lead him to dabble with such dangerous concepts.