Sakura could also be an ally. As a medic - ninja, she could help Kagome if she gets injured. And Sakura is used to dealing with strange situations and new people, so she would be open to helping Kagome.
I think Red Hood and Hawkeye could be likely allies. They both have a certain level of street - smartness. Hawkeye is used to working in the shadows and using his skills without relying too much on superpowers, just like Red Hood.
Kagome is a given as one of the main characters. She has her own set of friends and allies in the Inuyasha world, but in this fanfiction, the main focus would be on her encounter with Sesshommaru's pups. The pups themselves would be the other main characters. Depending on how the author writes it, there could be a lead pup among them, with a more distinct personality. And while Sesshommaru might not be present all the time, his influence would be felt through the pups. For example, they might have some of his combat abilities or his sense of dignity.
A jealous rival of Inuyasha might kidnap Kagome. For example, another demon who wants Inuyasha for himself might think that by taking Kagome, he can get Inuyasha to do his bidding. This would create a lot of drama and conflict between Inuyasha and the kidnapper.
I think Gaara could be an ally. Gaara has control over sand and is very powerful. He and Naruto have a mutual respect for each other. Additionally, Jiraiya. Jiraiya was Naruto's mentor and has a vast knowledge of different jutsu and combat techniques that could be used against Omega Shenron.
If the fanfiction is set in Columbia from Bioshock Infinite, Comstock would likely be the main antagonist. His fanatical religious beliefs and his plans for Columbia would clash with Kagome. Comstock wants to maintain his power and carry out his dark plans, and Kagome's presence, with her different way of thinking and her powers, would disrupt his carefully laid - out schemes.
Sasuke would be a likely ally. They have a long - standing relationship and have fought side by side before. Sasuke's Sharingan and his own unique abilities would be a great asset against the Ten - Tails.
Sakura and Sasuke are very likely allies. Sakura has her medical skills and combat abilities, and Sasuke, despite his past issues, has great power. They've been comrades with Naruto for a long time.
In a 'Kagome Meets Inutaisho' fanfiction, their meeting could be filled with tension. Kagome, coming from a different time and with her own set of beliefs and values, might initially clash with Inutaisho. However, as they get to know each other, they could find common ground. Inutaisho might be intrigued by Kagome's modern - day thinking and Kagome could learn more about Inuyasha's past through him. This encounter could also potentially bring about a new alliance or a deeper understanding between the two characters.
Inuyasha can be really interesting in this context. His reaction to Kagome's transformation into a Dark Miko would be complex. He's used to the normal Kagome, so seeing her change might make him both worried and a bit on edge. He could try to bring her back to her old self while also being in awe of her new power.
I think Sango would also be greatly affected. As a female in the group, she might feel a stronger sense of responsibility towards baby Kagome. She would be worried about how to take care of her properly, especially in their rather dangerous world full of demons. And she might also be concerned about how this would impact their overall mission and group dynamic.