Since Naruto has the Nine - Tails' chakra, which is a very powerful and positive energy source in the Naruto universe, it could act as a sort of shield against Darkrai's dark powers. On the other hand, Darkrai's ability to move between dimensions in the Pokémon world might give Naruto some insights on how to access different planes of existence in his own world, which could be a new power - up for Naruto in the fanfic.
Darkrai's power of inducing nightmares could be countered by Naruto's positive energy. Naruto's ability to inspire and his strong will could disrupt Darkrai's dark influence. For example, if Darkrai tries to put Naruto in a nightmare, Naruto's memories of his friends and his determination to protect them could break through the nightmare.
Naruto's godlike powers, such as his ability to create multiple clones or his Rasengan, could be used in combination with Medusa's stone - turning gaze. For example, Naruto could send clones towards an enemy while Medusa uses her gaze to turn some of the approaching foes to stone. This would create a distraction and allow Naruto to land a powerful Rasengan on the remaining enemies.
The clash of two different universes makes it interesting. Naruto has its ninja world full of jutsus and complex characters, while Darkrai is a mysterious Pokémon. Combining them can lead to unique storylines, like Naruto having to deal with Darkrai's nightmares or using his ninja skills to catch it.
Naruto's chakra could potentially enhance the werewolf abilities. For example, his strong life force chakra might make the werewolf's healing factor even more powerful. Also, his ability to use shadow clones could be used in a new way. He could send out werewolf - like clones during a full moon.
Naruto's god - like powers could enhance the Sekirei's abilities. For example, his chakra might be able to boost their elemental attacks if they have any. His ability to sense danger could also be transferred to the Sekirei, making them more aware in battles.
His chakra could potentially interact with the magic in the peerage. Maybe it could be combined in some way to create new and unique attacks. For instance, his chakra - infused rasengan could be enhanced with the peerage's magic for a more powerful blow.
Naruto's chakra could potentially disrupt the Devil Fruit powers. Since Naruto has a large amount of chakra, it might be able to interfere with the energy that the Devil Fruit gives Shiki. For example, if Shiki has a Devil Fruit that gives him the ability to create illusions, Naruto's strong chakra presence could break through those illusions.
I'm not sure of a specific 'naruto darkrai starter fanfic' off the top of my head. You could try searching on fanfiction websites like FanFiction.net or Archive of Our Own. They have a vast collection of fan - made stories, and you might find something related to Naruto and Darkrai there.
One idea could be that Darkrai enters the Naruto universe during a major battle. Its dream - inducing powers start to affect both sides, causing chaos. Ninja start to see their worst nightmares, and it becomes a race for Naruto and his friends to figure out how to stop Darkrai and wake everyone up from the nightmarish state.
Naruto might be initially in awe of Tiamat's powers. Given his curious nature, he would likely try to understand how they work. He could attempt to adapt some of her power - using techniques into his own ninja fighting style.
The Uzumaki clan is known for their strong life force. In a fanfic, this could enhance the use of the Rinnegan. For example, they might be able to use the Rinnegan's powers for longer periods without tiring. Their sealing jutsu abilities could also be combined with the Rinnegan's unique powers. Maybe they could create unbreakable seals using the Rinnegan's power.