Kaze and the Wild Masks

These achievements specifically require you to collect all bonus crystals in all regular levels. These come in the form of two teleporters hidden in each level, and each takes you to a mini bonus stage where you need to complete the criteria to be awarded half of that levels bonus crystal. Unlike all other collectibles, these two halves of the bonus crystal can be done on separate runs of the level, in case you miss one.

Speaking of which, these teleporters are by far the best hidden of all the collectibles. Many are pretty easy to spot them or where they could be hidden, but there were a bunch that were in completely unreasonable spots, in my opinion, where you'd absolutely never find them without a guide. As a result, don't be surprised if you need to use the videos below to mop these up.

For each bonus challenge, thankfully, if you fail, you are immediately given the option to retry; you don't need to retry the whole level or anything. The majority of these are pretty easy and just require coordination and dexterity with your movements, whether that be jumping, attacking, etc., and they typically are all very generous with the time you have. The only challenge is that a single hit fails the challenge in every case, so you have to be fast and careful. You get unlimited attempts though, so after a bit of practice all of these are very doable, and much easier than most levels.

Since you will assuredly need to check a video for some of these bonus crystal locations, refer to THIS PLAYLIST. These videos show all purple crystals, all bonus crystals, all KAZE letters, and show the level being completed without taking damage, cover all medals except the time trials. Full credit to the creator.