First, you should try to get away from the situation as soon as possible. Then, find someone you trust, like a teacher or another family member (preferably not related to the abuser), and tell them what has happened.
The status of manhwa hentai is quite controversial. It's not widely accepted in many communities due to its explicit and potentially offensive nature. Also, it may violate certain laws and regulations depending on the jurisdiction.
When your dad sees something private, it's important to remember that he is also a human being and has probably had his own share of embarrassing moments. You can approach the situation with a bit of humor. Say something like 'Dad, that was not meant for public viewing!' in a light - hearted way. Also, you can use this as a reminder to be more cautious about your privacy in the future. Maybe keep your door closed more often or be more aware of your body position when you are around family members.
First of all, it's important to stay calm. This is an accidental and embarrassing situation for both of you. Try to act as normal as possible and avoid making a big fuss about it. Maybe just quickly look away and pretend it didn't happen. If you feel really uncomfortable, you can later on find a time to have a private and honest conversation with your brother, just briefly mention that you hope this kind of accident won't happen again and that you both should respect each other's privacy more.
One reason it stands out is the detailed world-building and the unexpected turns in the plot. Also, the character development is really well done, making you root for the protagonist throughout the story.