One unlikely ally could be Zetsu. Zetsu is usually seen as a villain, but in a fanfic, he could have his own motives for helping Naruto defeat Pain. Maybe he wants to disrupt the Akatsuki's plans from the inside and sees Naruto as a useful tool for that.
Tsunade might be an unlikely ally in a different way. Usually, she's more of a support figure in the background. But in a fanfic, she could directly join Naruto in the fight against Pain. She could use her medical ninjutsu not just for healing but also in an offensive way, like creating chakra - infused attacks that catch Pain off - guard.
Sasuke could also be an unlikely ally. Given their complicated relationship, in a fanfic, Sasuke could realize that Pain is a greater threat to the ninja world as a whole. So, he decides to put aside his differences with Naruto for the time being and help him defeat Pain. This would create an interesting dynamic between the two characters during the battle.
Look to Chapter 187 for the clearest answer. It begins with During the competition, she passed by him numerous times, unfazed by..., keeps building through There was no visible trace of desperation on her face, yet her presence..., and lands on Perhaps it was a pig that tripped you;
Look to Chapter 200 for the clearest answer. It begins with Shang dismissed the thought of turning around and walking away., keeps building through The PD had already come over, and with the camera rolling, walking away..., and lands on Are you doing this on purpose?" Zhao Lang instantly put on an.
Look to Chapter 177 for the clearest answer. It begins with I'm actually the last?!" After the scores were announced, Wen Jiaojiao's..., keeps building through She slapped the table in disbelief., and lands on It was with great difficulty that she had gained a wave of fans in the....
The best chapter pointer here is Chapter 219, "Five Thousand Jin??!!". It opens with Qi Tianyu was somewhat freaking out. and closes on Having any yield at all was already the show giving them face..
Look to Chapter 203 for the clearest answer. It begins with Ah Fu knew he might have made a mistake, and after glancing at Su Yinwan,..., keeps building through The differing cries of the three children echoed around the stilt house,..., and lands on Su Yinwan's expression stiffened for a moment.
If you want the clearest chapter reference, go to Chapter 222. Early on, How come they're even live streaming in a reality show?!; later, the chapter leans on LOL, the expressions on these people, each one more skeptical about life....
If you want the clearest chapter reference, go to Chapter 215. Early on, Jiang Li let out a light sigh and tried to adjust her posture.; later, the chapter leans on I'm not dismissing you, I just think there's no need for you to cry." Wen....
Chapter 220 is the strongest chapter-level answer because it starts from I know everyone has many questions, and I'm here to answer them one by... and follows through on However, Su Yinwan and Shang Shaojing weren't particularly attentive to....
The best chapter pointer here is Chapter 219, "Five Thousand Jin??!!". It opens with Qi Tianyu was somewhat freaking out. and closes on Having any yield at all was already the show giving them face..
Look to Chapter 195 for the clearest answer. It begins with Jiang Yan was fully equipped and followed at the end of the team., keeps building through He was wearing a sports suit borrowed from He Yun, his face smeared with..., and lands on The audience and fans would definitely think she was.