In fanfiction where Dark Harry Potter joins Voldemort, how are the other characters' reactions portrayed?

The teachers at Hogwarts, like Dumbledore (if he were still alive in the fanfic), would be deeply concerned. Dumbledore always saw great potential in Harry for good. He would probably try to understand what led Harry to this path and would use all his wisdom and magic to try and turn Harry back. The other teachers would also be on high alert, fearing for the safety of the students and the future of the wizarding world.

His relationship with Hermione and Ron would be severely strained. They've always seen Voldemort as the ultimate evil, so Harry joining a 'good' Voldemort would be a huge shock to them. They might initially think Harry has been bewitched or something.

At first, Harry might be hesitant. But as he spends more time with Voldemort, he becomes more hardened. His values start to shift. For example, he may no longer see killing as an absolute wrong if it serves his new goals. His relationships with his old friends like Hermione and Ron will be severely strained. He'll become more secretive and calculating.

In these fanfictions, Harry's character transformation is quite drastic. He loses his sense of morality. His loyalty, which was once towards his friends and the good side, now shifts to Voldemort. He becomes more power - hungry, willing to do whatever it takes to gain more power, including using dark magic without hesitation. He also becomes more secretive and manipulative, using his former relationships to further Voldemort's goals.

Most fans would be shocked. Since in the original story they are enemies. This kind of fanfiction completely subverts the traditional relationship between them.

Yes, it is considered controversial. Harry Potter is traditionally seen as the hero who opposes Voldemort, the ultimate villain. The idea of him joining Voldemort goes against the core values of the original story. Fans of the original series often have strong emotional attachments to the characters as they are in the books, and this concept can be seen as a perversion of those characters.

Perhaps Harry joins Voldemort out of a sense of hopelessness. After seeing so much destruction in the wizarding world, he might think that joining Voldemort is the only way to end the war quickly. However, he soon realizes that Voldemort's methods are too extreme and tries to find a way to turn things around from within the dark side.

Often, Voldemort and Bellatrix's relationship is shown as one of master and devoted servant. Bellatrix is extremely loyal to Voldemort, almost to the point of worship. She will do anything he asks without question.

One possible plot could be that Harry, influenced by his darker side, joins Voldemort to gain power. He might start to learn the Dark Arts from Voldemort directly. Another plot could be that Harry believes Voldemort has some secrets about his family that he can only learn by getting close to him. Also, it could be that Harry is tired of the Order's way and thinks Voldemort's methods are more efficient in achieving his own goals.

Ron would be extremely angry at first. He might feel betrayed by Harry. But as he realizes that something must be seriously wrong with Harry, he would probably join Hermione in trying to save Harry from Voldemort's influence. They would look for a way to break whatever spell or false belief has hold of Harry.