Naruto could be one of his allies. Naruto has this knack for seeing the good in people and would probably be willing to give Obito a chance to redeem himself. Also, Sakura, with her skills as a medic - ninja, could be an ally. She might help heal Obito if he was injured during the war and see the potential in him to be a force for good.
I'm not sure as I haven't read it specifically. But generally, a 'regressor' in novel terms might imply a character who goes back in time or reverts to a previous state. So perhaps this novel is about a character who is not such a regressor and has a different kind of story, like a forward - moving adventure or a story based on present - day challenges.
One possible motive could be to use Sakura as a bargaining chip. If he has some sort of plan against Naruto or the Hidden Leaf Village, Sakura, being a close comrade of Naruto, could be very useful. He might think that by restraining her, he can force Naruto to come to a certain location or make concessions.
One popular sakura and obito fanfiction is 'The Unseen Bond'. It delves into a world where Sakura discovers Obito's hidden past and tries to help him find redemption. Another great one could be 'Sakura's Encounter with Obito', which focuses on their chance meetings and how it gradually changes their relationship. And there's also 'A New Path for Sakura and Obito' that shows them working together to face challenges in the ninja world.
The sad story of Obito and Rin is a key part of the Naruto narrative. Obito was a young ninja with big dreams and a huge crush on Rin. When Rin was seemingly killed in front of him, it shattered his world. He thought that the ninja world was full of pain and betrayal. This led him to be influenced by Madara. He became one of the main antagonists, all because of his love for Rin and the unbearable pain of losing her. His journey from a hopeful young ninja to a vengeful villain is a tragic consequence of Rin's death.
Sadly, I'm not aware of the author of 'im the max level newbie novel'. There are so many novels out there that it's difficult to know every author. You could also try reaching out to local libraries or bookstores to see if they have any information on it.
I'm not sure specifically as I haven't read it. But generally, a 'newbie' in a novel often refers to a new or inexperienced character. And'max level' might imply that this newbie has reached an extremely high or top - level state in some aspect, perhaps in power, skills or knowledge within the context of the story.