Well, you could look for manga on platforms that offer offline download options. For example, some subscription-based services allow it. Just make sure you have enough storage space on your device and a stable internet connection for the initial download.
First, make sure you have the game downloaded. Then, look for the offline mode option within the game settings. It should be straightforward from there.
Then there's 'The Room' series. These are puzzle games with an overarching mystery story. You explore strange, detailed rooms and solve intricate puzzles to unlock more of the story. The atmosphere is very spooky and the story is full of twists and turns.
You might find offline manga reading options on dedicated e-readers like Kindle or Kobo. Some manga publishers also release digital editions that can be downloaded for offline viewing. Also, check if your local library has digital manga collections available for borrowing offline.