Well, Sirius is a complex character. His reaction would depend on his relationship with Lily at that point in the fanfic. He could be overjoyed, seeing it as a new chapter in their friendship. He'd probably offer his help right away, whether it's in terms of finding a good place for her to stay during the pregnancy or just being someone she can talk to when she's feeling worried or scared. He might also feel a sense of protectiveness towards her, vowing to keep her and the unborn child safe from any harm.
Sirius may react with a mix of emotions. At first, he could be stunned into silence for a moment. After that, his loyalty to his friends would kick in. He'd start making plans to help Lily, like ensuring her safety and thinking about how to support her through the pregnancy both emotionally and practically.
One possibility is that Sirius helps Lily break the news to James. This could lead to some tense moments if James wasn't expecting it, but also to a strengthening of their relationships. Another could be that Sirius starts looking into ways to protect Lily from any threats during her pregnancy, perhaps suspecting some dark forces might be interested in the unborn child.
Gray could be a mix of emotions. On one hand, he might be happy deep down but also feel a bit scared about the responsibility that comes with having a child. He might start stammering as he tries to find the right words to say to Juvia.
Sirius might be shocked. He'd probably feel a mix of horror and protectiveness. He'd be horrified that Voldemort has used Harry in such a way and would be even more determined to keep Harry safe from Voldemort's clutches.
Well, Sirius is a very protective character. When he discovers that Harry is a Horcrux in the fanfic, he could initially be in denial. But once he accepts it, he'd likely start looking for ways to either protect Harry from Voldemort or find a way to remove the Horcrux part from Harry. He might also feel angry that Harry has been put in such a dangerous situation.
Sirius would probably be shocked at first. Then, he'd likely feel a deep sense of sadness and guilt. He might think that he should have been there more to protect Harry from getting those scars.
James might be overjoyed. He could immediately embrace Lily and start talking about their future together, like planning for the baby's room or thinking about names.
Sirius would probably be very concerned. He might immediately ask her what's wrong and offer her a handkerchief to dry her tears. He has a bit of a wild side, but he also has a big heart, especially when it comes to those he cares about or sees as in need of help.
He probably reacts with a mix of emotions. Mulder is a complex character. He might immediately start thinking about all the implications, like how this will affect their work and their lives. He could also feel a deep sense of protectiveness towards Scully and the unborn child right away. His reaction might be one of those silent, but very profound moments where he just looks at Scully with a whole new level of understanding and connection.
Sirius's friends, like the Marauders, would be extremely shocked. They would probably be very concerned about Sirius as they know his feelings towards Bellatrix as an enemy. They might try to convince him to break away from the situation, thinking it's some sort of dark plot against him. James, in particular, would be very protective and would want to figure out what's really going on.
There are fanfics where Sasuke is a bit more reserved in his reaction. He may not show extreme emotions outwardly but instead, internally he's filled with a mixture of excitement and fear. He might start thinking about all the responsibilities that come with having a child and how his life as a ninja will need to change to accommodate this new addition to his family.