It depends. Some manga reader apps are legal if they have the proper licenses and permissions to offer the content. But many are not, as they violate copyright laws.
MangaZone is a good one. It has a large collection of manga, and the search function works well. The app is easy to navigate, making it convenient to find and read your favorite manga.
You need to start with a solid programming language like Java or Python. Then, focus on creating a user-friendly interface and integrating a reliable image viewer for manga pages.
The safety of a manga reader app varies. You should look for apps from trusted sources, read reviews, and check if they have proper security measures in place. If an app looks sketchy or asks for too much personal info, it's probably not safe.