There may be. There are fanfic communities that strive to create content suitable for a wide range of audiences. In the case of an 'eren gets mikasa pregnant fanfic', it could be written with themes like family values, the growth of their relationship, and the anticipation of new life. For example, it could detail how Mikasa's character might change as she prepares to be a mother, and how Eren steps up to support her, all while keeping the story appropriate for all ages.
Another possibility is a jealous rival. Maybe there's someone who is jealous of Gohan's power or his relationship with certain characters. This rival could do things to annoy Gohan and push him to the edge of his temper.
A new player on an opposing team could be the cause. This new player might be overly cocky and disrespectful towards Kuroko during a game. They could constantly taunt him about his lack of presence, which finally gets on Kuroko's nerves and makes him mad.
It could be Vegeta. Maybe Vegeta does something really underhanded like stealing Goku's senzu beans or trying to take all the credit for a victory that Goku also contributed to. Goku, being a fair - minded person, would get angry at such behavior.
One of his friends could be the cause, accidentally. Maybe a friend makes a deal with a shady character without realizing the consequences. This deal ends up putting everyone in danger, and Yami gets mad at his friend's naivete and the mess they've created.
He might become withdrawn at first. Since he's used to being in control and having a certain dynamic in their relationship, Bella's anger could shock him into pulling back. He could go off on his own for a while to think about what he did wrong.
The main characters are obviously Eren and Mikasa. Eren is often portrayed as a complex character with strong will and determination. In this fanfiction context, he will be dealing with the new situation of becoming a father - to - be. Mikasa, on the other hand, is a strong - willed and loyal character. Her pregnancy will likely bring out different aspects of her personality, such as her nurturing side.
Definitely Doofenshmirtz. He could mess with one of Phineas and Ferb's inventions in a way that really ticks Phineas off. Like he might use one of his -inator devices to turn their amazing flying machine into a pile of junk. Phineas would be furious and would then set out to fix it and get revenge on Doofenshmirtz.
It could be his rival. Rivals in Yu - Gi - Oh are always trying to one - up each other. If his rival manages to steal a rare card that Zane has been eyeing, or if the rival taunts Zane about a recent defeat, that would surely make Zane mad.
A common theme is protecting loved ones. When Trunks sees his family or friends in harm's way, he gets mad and is driven to take action. Another could be revenge. If someone wrongs him or his loved ones, his anger fuels his desire for revenge in the fanfiction.