Some general advice for using the My Fairy mode.

So decided to do a generic write up based on my findings in the Japanese game. May have been posted already but I hope this helps somebody.

Getting Started:

To be able to access the "My Fairy" mode you need to first unlock a fairy. This is done through adventure mode and the tiles with them will always have a small a fairy icon in their rewards list. If it has something akin to a clothes item, or a giftbox on the general map, that means there are clothes in the map. While I don't recall the exact locations there are a handful of fairy on each adventure map. There is one for each elemental type: water, light, dark, fire, and lightning. Just search keeps. Brown jars contain fairies, while capturing a keep will give you a chest with the clothes inside. Food is also found inside brown jars, and once you find food via this manner enemies will begin to drop it. Food found in this manner is always higher quality, while dropped food is more often of lesser quality. Fairies on different maps will have different hair style/colors and differ in personality traits. You can hold 5 initially, but gain one more slot upon clearing each adventure map. If you find too many fairies you can replace one you don't want anymore. You can double up on fairies of the same element if you so wish. A barrier fairy you save in a keep does not count.

Personality Traits and leveling:

The personality stats change which rental skills you can learn. For example, some higher level skills will require stats not often found in early game fairies. To compensate for this you can refresh a fairy after feeding/leveling it to 99. You can change a single trait every refresh. Would advise against grinding food to change to desired traits, as early game food doesn't really boost traits needed for higher level skills(like Magic Fountain).

Higher level rental skills include things like Magic Fountain(endless magic for a little while), or Keep Repair(which restore your base/a keep to max hp). You set these to your item slot and use them according, while tapping the fairy icon will release a shockwave burst if you have enough magic. These attacks kill everything in the area not an officer, even invisible un-rendered enemies, and make "get lots of kills" missions a snap. Combining this with the unlimited magic allows you to rapid-fire. It's pretty broken, but you probably wont be able to do it until very late into the game. Other skills change how drops work/make enemies slower etc... When a fairy levels up to 25/50 she gains an elemental attribute based on how she was fed. Darkness, for example, slowly saps health from every enemy over time in the area you used the burst. Fire lowers defense, and so on and so on. Different food will increase different elemental attributes, but early food tends to favor light and water.

Every 25 heart levels they will gift you a weapon/rupees/rare materials. If you decide to release a fairy that has been raised a decent amount, you get a gratitude crystal of it's element. Raises 10(12 if element matches) in all current personality stats.

Refreshing:

When a fairy reaches level 99, you get the option to refresh it. This resets the fairy to level 1, allows you to rename it, and lets you change a single trait. You keep a fraction of your gains with each refresh, and all rental skills are retained even if you replace a needed trait. The fairy keeps their progress in any trait you decide to replace. The burst attack also gains some power with each refresh, and you can feed it different food to change what its elemental burst becomes.

Clothes:

When you see a giftbox on the map, or a clothes like item in the rewards tab, there is a chest hidden in a keep with a single wearable item. These usually add different elemental damage to the fairy burst or decrese the cost to use it. Clothes tend to go thematically by map with the only exception being Skyward Sword items, which are on the stock adventure map and master quest. Most items have variants of different colors for each elemental type.

If you have any further questions, please feel free to ask.