Well, one possibility is that Dark Naruto would be overjoyed. After all, Kushina is his mother. But at the same time, he could be very conflicted. His dark side might make him suspicious of her motives. He could test her in various ways to see if she's really who she says she is. And Kushina, on her part, would probably be heartbroken to see what her son has become.
It could develop in a complex way. Maybe at first, Kushina is shocked by Naruto's dark transformation. But as a mother, she tries to understand him. She might start by reaching out to him, trying to find the root of his darkness.
In the 'dark naruto abandoned by kushina fanfic', Naruto could be shunned by the village due to his mother's abandonment. This isolation drives him to the dark side. He may learn unique and forbidden jutsu from mysterious sources. His goal could be to reshape the ninja world in a way that would make those who abandoned him regret their actions. He might also have internal struggles between the remnants of his good nature and the new - found darkness within him.
The main antagonist could be the Hidden Leaf Village itself. Since Naruto was abandoned by Kushina, the village that failed to take proper care of him could be seen as the enemy. The village elders or those in power who turned a blind eye to his suffering could be the ones he has to oppose.
Dark Naruto could be characterized as more brooding and cynical. Instead of his usual optimistic self, he might be distrustful of others due to some past betrayal. His powers might be more uncontrollable, with the Nine - Tails' influence being more prominent. Dark Kushina could be shown as a fierce and unforgiving figure. She may be highly protective of Naruto and willing to do whatever it takes to keep him safe, even if it means using extreme measures.
It's difficult to determine the popularity of this particular fanfiction. There are so many fanfictions out there in the Naruto fandom. If it has a unique and engaging story, it might be popular among those who are into darker interpretations of the Naruto characters and stories. However, it could also be relatively unknown if it hasn't been promoted well or if the theme is too niche for most fans.
One possible fanfic could be about Kushina's early days in the Hidden Leaf. It might explore her training as a ninja, her relationships with her peers, and how she was perceived in the village. Maybe it delves into her friendship with Mikoto and how they supported each other during their pregnancies.
One possible reason could be that Dark Naruto might see Kushina as a symbol of the world that rejected him. Since she was an important part of Naruto's family and the village, and Dark Naruto represents Naruto's negative emotions, he could resent her for the life he didn't have. He may feel that if Kushina had been there for him more (in his twisted view), he wouldn't have turned into this dark version.
One thing that could happen is that Dark Naruto would be filled with a mix of emotions. He could be angry at the village for hiding this from him, yet also feel a glimmer of hope. This discovery might make him question his loyalty to the forces that led him to become 'dark'. He might also feel a sense of longing for the family he thought he had lost.
Often, it portrays Dark Naruto as extremely bitter. He may be shown constantly thinking about Kushina in a negative light, with his every action towards her being full of malice. For example, he might plot revenge against her, even though she is dead in the original story.