Perhaps a teacher at Hogwarts. If Sirius has been misbehaving in a way that the teacher thinks is unacceptable, they might send a howler as a last - ditch effort to get him to behave. However, this would be quite an extreme measure for a teacher to take.
His mother could send the howler. In the wizarding world, mothers can be quite fierce when it comes to family reputation and she might be unhappy with Sirius's actions or friends.
It could be an old family acquaintance. Maybe someone who is trying to keep the Black family in line with their pure - blood traditions and sees Sirius as a threat to that. So they send a howler to try and intimidate him into conforming.
Chapter 26 is the strongest chapter-level answer because it starts from Shen Lan was bent over processing a large stack of press briefs on her... and follows through on If you think you can use our family connection to have me handle this....
Chapter 2 is the strongest chapter-level answer because it starts from On the top floor of the Financial Building, a gathering of dark clouds... and follows through on Jiang, Lin Manru, turned pale and quickly explained, "It's not eloping, my....
A practical answer is Chapter 11, because it turns the idea into a concrete scene. The chapter opens with After a meeting, Shang Shaojing pinched the bridge of his nose, tired, and..., adds pressure through Qin, could you pour me a cup of tea as well?, and ends on Miss Qin, please accompany us to.
Look to Chapter 5 for the clearest answer. It begins with Actually, when Manager Fang saw Jiang Li, he was somewhat surprised., keeps building through Because she was really too beautiful, and very young, completely different..., and lands on Recently, he did suspect that his wife was cheating on.
Chapter 718, "This Person Is No Longer the Same Person", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. The chapter turns that into something concrete by moving from Changqing noticed her amazed gaze and his eyes also shifted to the...
Chapter 688, "Iron Sand Palm Skill Acquired!", is the clearest early answer because the violence around Luo Xingmu becomes final instead of hypothetical. The chapter turns that into something concrete by moving from Shao Changqing was very pleased with Bai Lu.
Chapter 901, "Your Wonderful Future Has Just Begun", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event.
Chapter 902, "Sister, Please Have Your Meal", is the clearest early answer because it turns Shuiyun Mountain's situation into a concrete plot event.
Chapter 904, "Welcome Young Master and Young Madam!", is the clearest early answer because it turns Jiang Bufan's situation into a concrete plot event. The chapter turns that into something concrete by moving from Jiang Bufan and Jiang Buchen immediately ran up in surprise.
The best chapter pointer here is Chapter 10, "All for Wiping Your Butt". It opens with Qiao's shocked face struggle to recover, Lin Manru also tasted for the... and closes on Who was it again saying that the Jiang Family's tradition was lacking,....