In superstar mode, reach level 2 with Arareru, this is at 50,000XP. A good score on a song can net you up to around 2500XP, there is nothing to this achievement, just keep singing songs, any will do, after choosing this character. The order is always the same: 3 of your choice, out of a small list, then 2 chosen at random by stopping the numbers like a slot machine, then finally 1 more song by stopping a spinner, everyparty style. None of these options matter for this achievement, just keep on singing songs for XP.
In superstar mode, reach level 3 with Fuzurugun, this is at 120,000XP. Same applies as for the achievement above ^.
This is for unlocking the Hujulgeun character, this is done by singing well with Arareru, after I got a couple of 100 ratings with Arareru this just popped right up. If it doesn't just keep playing as it will pop up very early.
S 등급 연속 획득
Very simple; just get S rankings on 3 songs in a row, you don't even have to do particularly well in this game to get an S rank. Just hit most of the notes and you should be good for an S rank, the score doesn't seem to be greatly related to the rank either as you can have an S rank with a score of 65 but a B rank with a score of 80+. I think the rank is to do with the percentage of notes hit and score is the ratings you get: Great, Good etc
게임 판정 도전
Get all greats on a song. By far the hardest achievement in the game, and about the only one you may not get from grinding out songs. Now song 'selection' is a huge part of this achievement as I couldn't often get a Great rating on the shortest of notes, so you have to hope for a short song with no short notes to come up. The second method is to find an english song you can do well in and practice it then when you start a new 'Gig' if it isn't in the list of songs, hit B then A and the list refreshes with a new selection. Without this achievment the game would be an easy 1k, this will require luck and patience. Remember, must be done in Superstar mode as well.
레전드 랭크 달성하기
Reach Legend rank with the Dog: this is achieved at 720,000XP. Again there is nothing to this achievement but a long grind, just keep using the Dog. I'd estimate around 300-400 songs. To unlock the Dog character, as stated in the Roadmap, use all the other characters once. This is probably the longest achievement, but there is no luck involved which is nice.
The XP required to level up is as follows:
Level 1: 0XP
Level 2: 60,000XP (50,000XP for Arareru)
Level 3: 120,000XP
Level 4: 240,000XP
Level 5: 480,000XP
Level 6: 720,000XP
티아라의 노래 교실
Tiara's Singing lesson; get a 100 rating on 3 consecutive songs using Tiara. This achievement is misleading, as, from my experience, they don't need to be consecutive just as long as at least 3 of 6 songs in the Gig are 100 ratings, this will pop. This is not a problem and you will often get 6/6 songs at 100 rating. You needn't get all Greats to get this rating but just need to do pretty well and hit at least around 99% of the notes. There are many songs which have weird parts which you will get many misses, however this doesn't appear to affect the rating, as long as you clear the song.
Unlock all characters, very straightforward, the characters are unlocked as follows:
Arareru: Available at start
Fuzurugun: Available at start
Hujulgeun: Do well with Arareru or just do many songs
Tiara: Do well with Fuzu or just do many songs
Grandfather Kumoni: Reach level 4 with any character (at 240,000XP)
Dog: Complete a 'Gig' with all other characters
Endurance:towards the legend. Once you have opened up the last 'Gig' with the Dog as you are leveling him up, keep doing it. Choose it every time and complete it 10 times in a row without backing out, failing, switching off your console etc etc. It sounds worse than it is, just hope that you get 60 songs which aren't impossible to pass (there were a few I could never manage which had odd bits which went to miss straight away). However, I never encountered these while playing as the Dog. This is simply perseverance, can be done on the way to the Legend Dog achievement.
Lucky Nabaru, or lucky Grandfather Kumoni; the achievement says it all, you have to get really lucky. While playing as Grandfather Kumoni, you need to have 'item' appear next to 5, then land on 5 when using the spinner to choose the 6th song of the 'Gig'. Persevere and try not to back out of a gig as it may block this achievement. One in 150 song chance of getting this one as stated in the roadmap but nothing really hard about it, just keep completing songs.