hey everyone~
this event's last bosses were extremely hard, but I finally figured out how to beat the last Ice boss.
At first I wrote one build, but after consulting with my friend who found out a better build, I did some changes in mine too. I'll show both her and mine, and you'll choose what you can~

Both of the builds will require some stage girls that most of you should have from past events or ads gacha + one girl who is GP Ichie or a tank, respectively.

First Build: 3 Damage Dealers, one of them is Ichie who is a semi-tank

This build will use Pirate Lalafin as frontal tank, GP Ichie as a damage dealer/second tank, Nurse Yachiyo for damage buffing only, Elena Nana from the mafia event and Fairy Godmother Aruru from the Cinderella event as damage dealers.

Example Video
Thanks, TsUNaMy WaVe~

Keys:

• Elena Banana + 1 Fortitude memoir.
  Main damage dealer at the start of the battle. her gimmick is to taunt the enemy at the start of the battle for two rounds, and then use her 3AP and Climax to deal INSANE amount of damage. a 6* rank 7 Elenana with at least 1 fortitude memoir should survive EXACTLY the six attacks of the boss, which make her in her best shape to deal maximum damage with her 3AP and Climax for the rest of the battle.
  You should prioritize her 3AP and Climax over the other damage dealers when you can, and only after the boss bring her to 1HP.
• Ghost Patrol Ichie
  A very balanced unit who can play both the roles of a damage dealer and a secondary tank.
• Pirate Lalafin + Fortitude Memoir.
  An excellent Wind NDEF tank for this boss. you should avoid using her ACTs and prioritize the damage dealers.
• Fairy Godmother Aruru
  A great damage dealer. you should prioritze her 2AP attack, and aim to climax just before the boss is about to climax. if the stop effect procs, you'll cancel its climax entirely~
• Nurse Yachiyo.
  For Damage buff only. DON'T USE HER HEALING ACTS. it'll only weaken Elenana.
• Guest: Nurse Mei Fan. Damage buff + climax.
• Note: all stage girls should be at least rank 7 and fully potential bloomed.

Second Build: 2 Damage Dealers, 2 Tanks

The general idea is to use TWO TANKS (one is Pirate Lalafin, and the other is varied), Elena Nana from the mafia event as your main damage dealer, Fairy Godmother Aruru as a secondary damage dealer (because a ratio of "1 damage dealer : 3 Tanks/Support" is awful for damage dealing ACTs chance), and Nurse Yachiyo for damage buffing. This build will not require GP Ichie that some of you may not have, but instead you'll use any other tank who can take enough damage until Elenana and Aruru kills the boss. I used Moriarty Mahiru as the second tank, but you should use Belle Shiori if you have her. if not, you I believe you can use YJ Rui and spam her barrier buff, or maybe even SN Maya. try what works for you~

Example Video

Keys:

• Elena Banana + 1 Fortitude memoir.
  Main damage dealer. her gimmick is to taunt the enemy at the start of the battle for two rounds, and then use her 3AP and Climax to deal INSANE amount of damage. a 6* rank 7 Elenana with at least 1 fortitude memoir should survive EXACTLY the six attacks of the boss, which make her in her best shape to deal maximum damage with her 3AP and Climax for the rest of the battle.
  You should prioritize her 3AP and Climax when you can, and only after the boss bring her to 1HP.

• Pirate Lalafin + Fortitude Memoir.
  An excellent Wind NDEF tank for this boss. you should avoid using her ACTs and prioritize the damage dealers.

• Belle Shiori | Moritarty Mahiru | Yagyuu Jyuube Rui
  Another tank beside or in front of Lalafin. I tried it with Mahiruiarty and with Lalafin they gave me enough defense to kill the boss with Elenana and Aruru. I'm sure Belle will do even better than Mahiruiarty, especially with her excellent climax that puts the boss to sleep and cancels its climax. I haven't tried, but I believe that YJ Rui should do fine too as the best NDEF tank in the game, although she isn't wind attribute. and if you don't have anyone of those options, maybe SN Maya will suffice... but I'm really not sure about her.

• Fairy Godmother Aruru
  A secondary damage dealer. you should prioritze her 2AP attack over Elenana 2/1AP, and aim to climax just before the boss is about to climax. if the stop effect procs, you'll cancel its climax entirely~

• Nurse Yachiyo.
  For Damage buff only. DON'T USE HER HEALING ACTS. it'll only weaken Elenana.

• Guest: Nurse Mei Fan. Damage buff + climax.

• Note: all stage girls should be at least rank 7 and fully potential bloomed.

okay, I figured out how to beat the last Moon boss quite easily. it'll be similar to the "2 damage dealers and 2 tanks" build of the Ice boss, just with Musketeer Hikari as main damage dealer, Musketeer Karen as secondary damage dealer, Benkei Tamao as main tank, Nurse Yachiyo for damage buff, and lastly - a varied SDEF secondary tank.
The general idea is to use Hikari's 2AP ACTs as much as you can to deal a lot of damage with her attacks and climax, and to stack as many evasions as possible before the boss reach her (and it should die around this time), and Karen here to cover the damage dealing per turn (as it's not likely we'll get Hikari's acts every turn).

Example Video

Keys:

• Musketeer Hikari + 15% Elemental Effectiveness memoir.
  Main damage dealer. you should prioritize her ACTs as much as you can. her 2AP brilliance attack is great for building her devastating climax, and her 2AP 'evasion + act power up' is great for stacking evasions for the moment the boss will reach her.
• Benkei Tamao + Fortitude Memoir.
  Your best easy-to-get tank against this boss. do not use her ACTs if you can. all her acts are worthless damage dealers. you should focus the climax building on Hikari (you can see in the vid that I could use her climax and gave up on it to not lose the two 2AP acts of Hikari that I got on this turn).
• Heracles Michiru | Moritarty Mahiru
  I used Mahiruiarty and my friend used Michiru with this build, and both of them were great for the role of secondary tank. don't panic, you don't really need them specifically. you can put your highest Special Defense non-space unit with fortitude memoir and I believe it'll be enough. I believe that even the Black Lion Claudine that everyone should have from the ads gacha will do the job~
• Musketeer Karen
  A secondary damage dealer. her climax is much less powerful and important than Hikari's, so you should prioritize Hikari's acts over Karen's when you can, and prioritize Karen's acts over the rest of the unit. we use her to balance the damage dealing (one damage dealer with 3 tank/support really screw the damage dealer acts chance).
• Nurse Yachiyo.
  For Damage buff only. Unlike with the Ice boss, here you can use her healing acts, but I suggest still prioritize Hikari's and Karen's when you can.
• Guest: Nurse Mei Fan. Mostly for damage buff. her climax is less important here.
• Note: all stage girls should be at least rank 7 and fully potential bloomed.

Well, that's it. good luck everyone! ^~^