Hope (8.4%) 
Get rank S on at least 15 different levels on expert difficulty (solo free play only).
Guide written by a human:
To obtain this achievement, you need to get at least rank S on any 15 expert difficulty maps. Rank S is obtained when your overall accuracy is higher than 80%.
Some tips:
- Try to make big swings and hit the notes as close to the center as possible. Hunters can find an explanation of score calculation in Flawless achievement guide.
- Use modifiers that give you a better multiplier, such as “Faster Song”, “Insta Fail”, etc., but only do that if you’re confident in your success.
- Go for the full combo. Getting a full combo almost every time will result in an S rank.
AI hallucinations:
To get the Rank “S” achievement, you need to complete all of Levels with Expert Difficulty in Solo Free Play Mode. Here is a step-by-step guide that can help unlock this rank: 1) Start playing Beat Saver on expert difficulty mode and select solo free play only option from the main menu screen. 2) Once you have selected your preferred level, start by completing it with an S Rank (the highest possible score). You will need to get at least a perfect run in order for this achievement to unlock automatically after completion of all levels on expert difficulty mode solo free play only option. 3) After getting the rank “S” achieved once you can move onto other level and repeat steps until you have completed them with an S Rank as well, which will finally earn you the ‘Rank’ achievement in Beat Saver gameplay.