Some tips:
- Daily reviews will almost certainly continue going up, but so your ability to do more reviews in less time. So it doesn’t necessarily get harder in my opinion.
- Try to leave 0 reviews before going to bed. This way, you won’t have reviews piled up from the previous day to make your following day harder.
- Do WK around 3 times a day if you can (morning, lunch time, evening).
- Read my Guide for Wanikani, if you haven’t already. Mainly chapters 4-7: