There could be. Given the creativity of fanfiction writers, they might find interesting ways to blend the Naruto universe with the Sonic universe, specifically with Metal Sonic. It could involve Naruto being transported to the Sonic world and having an encounter with Metal Sonic, or perhaps some sort of power - related connection between Naruto's abilities and Metal Sonic's characteristics.
For Amy, she could become more understanding of the 'evil' or opposing side. Instead of just seeing Metal Sonic as a bad guy, she might learn to look deeper into his existence as a creation. This could make her more empathetic in general.
I'm not sure about its popularity. It depends on the fan community. Some might find the dark and edgy concept interesting, while others might not like the idea of Tails being killed off in a fan - made story.
One idea could be that Metal Sonic somehow gets transported to the Naruto universe. He might be mistaken for a strange new type of summon by the ninja. Metal Sonic could then use his speed and robotic abilities to cause chaos or, alternatively, befriend some of the ninjas who are intrigued by his technology.
A 'Metal Sonic x Shadow Fanfic' might explore an interesting dynamic between the two characters. It could involve their unique abilities interacting in different scenarios. For example, Metal Sonic's robotic precision and speed combined with Shadow's chaos powers could lead to some really intense action scenes. Also, the fanfic might delve into their personalities, perhaps showing a rivalry or an unexpected alliance.
One common theme is redemption. Many fanfictions explore the idea of Metal Sonic being redeemed through his interactions with Amy. For example, Amy's kindness might make Metal Sonic question his evil programming.
In fanfiction, Metal Sonic often interacts with Tails as an adversary. Since Metal Sonic is usually programmed to oppose Sonic, and Tails is Sonic's friend, Metal Sonic sees Tails as an obstacle. For example, he might try to attack Tails to get to Sonic or to stop Tails from helping Sonic in a fight.
The plot might be centered around a power - hungry or misprogrammed Metal Sonic. Tails could be in the middle of working on a project that could potentially stop Dr. Eggman for good. Metal Sonic is sent to stop this from happening by any means necessary, which unfortunately for Tails means death. It could also explore the emotional aftermath among Sonic and his friends, like how Sonic would react to the loss of his dear friend Tails. There might be a revenge plot where Sonic then sets out to destroy Metal Sonic once and for all.
Naruto might be initially scared or very curious about Metal Sonic. He'd probably try to talk to him or challenge him. Metal Sonic, being a robotic creation, would likely be confused by Naruto's behavior. He might see Naruto as a threat or just an oddity at first.
One possible plot could be that Naruto is somehow transported to the Sonic universe. He encounters Metal Sonic, who mistakes Naruto for a threat. Naruto, using his ninja skills, tries to communicate with Metal Sonic but fails. So, he has to use his combat abilities to defend himself against Metal Sonic's attacks while also trying to find a way back to his own world.