Chain Kill Master
Achieve a Chain Kill of 100 or more.
Every time you kill an enemy, a counter above your chosen character's head will increase. This is the Chain Kill counter. It will keep increasing until you are unable to kill an enemy within 3 seconds of your last. While it has little influence on any in-game mechanics, only restoring your HP and MP fully every 50 kills (it doesn't even act as a score multiplier!) it's still satisfying to see it rise, isn't it? To unlock this achievement, you'll have to reach a Chain Kill count of 100.
There are only a few places to attain this feat, and it's worth noting that Score Attack is not one of them. You can actually get this as your first achievement because there are two areas in Stage 4 where it is possible, as well as in Chain Kill Mode, but the easiest place in the game to unlock this is obviously the end of Stage 5-5 - Rudderless Voyage. Just over 175 exploding hornets will attack you, and with one of Nive's MoonSault Combinations, getting a 100 Chain Kill is an absolute joke.
Save your companions 10 times in a single game.
When a player dies in a co-op game, they float around above where they died, ensnared by chains. Attack them a few times with
to Rescue them. Perform the action 10 times in a single session (read: without leaving the lobby or going back to the title screen) to unlock this achievement.
Raise the average level of all characters to level 50.
This achievement requires some simple math and a lot of grinding. To figure out your current average level, add the levels of all four characters together, and divide by the number of characters.
To make it even easier, skip the math: you'll unlock this achievement when you've acquired 200 levels total, across all four characters.
When grinding, avoid using charge attacks as you are awarded EXP for each hit on an enemy. Note that some MCs may not give you EXP despite dealing damage to enemies, so avoid using those. In general it is a better idea to avoid using MCs because they are often more powerful than your default attacks. Nive's MCs are typically a great idea though, as they are quite weak and also help you catch an extra enemy before it teleports away once in a while.
Stage 12 and Chain Kill Mode provide the highest concentrations of enemies in the game, and Stage 9 contains many Planet Blaster Cannons.
Collect 50 MC techniques.
MC is shorthand for MoonSault Combination. Essentially the game's take on the typical magic spell or "special attack," MCs are collected from yellow crystals stashed throughout the game's stages in specific locations. Multiple MCs may be hidden in a single sub-stage, and even though every character starts out with a different MC (Silence starts with two!) each character can obtain every MC. Locations and MCs acquired do not change between characters. To unlock this achievement, you will need to find 50 of the game's 60 MCs.
Check out this post
in the companion thread for the locations of all the MoonSault Combinations.