There's an app called "Memory hint", and please, don't download it if you have photosensitive epilepsy or at least consult with a professional, because there's "Kanji catch" mode that could POSSIBLY trigger a seizure, at least if you won't lower speed. I almost had a seizure because of it.
Please, be careful with apps and videos you're watching, because sometimes there's no TW!
Just accept the fact that flash warning doesn't count as a warning when it appears on a 0,1 second with a small font in the bottom of the screen. I hate it when people can't take a minute to make a good tw.