Hello there!

The game is already done, but I want to continue to talk about some "secrets" and stuff inside the game that perhaps some of you missed since are not that evident at first sight. This time, I'd like to give you a guide to a special set of equipment you can obtain fighting special enemies that resemble the current members of Holostars (minus the latest Gen) present in the game, where you can find them and what kind of Equipment they give you.

SPOILER WARNING!!!! Don't read if you don't want spoilers for the story, but if you don't mind, you can go ahead!

These enemies can be found in each of the Void areas (available after obtaining Coco) near some ominous statues that are spread across the different places. Some statues have a little higher chance of spawning these enemies. These drop "Cores" that, once they reach the number of 50, fuse together to create the equipment. Each time you defeat one of these, they drop one Core, but you can also steal another one from them or their companion in the battle to make the progress faster. This is some quite heavy grinding so it may not be your thing, but the weapons would make battles really easy to affront and it gives some achievements as well so you can try if you like that!

1. Void Demon: The first one to appear in the first available Void area (where you save Anya), which resembles Aragami Oga. Collecting 50 Bull Demon Cores from him gives you the DemonSlayer (Dagger, +200 Atk +200 Sp.Atk + 1 Attacks Void Element / Blindness, Poison, Charm, Seal, Sleep, Confusion Immune) and the Demon Mask (Head Armor, +100 Sp.Def +100 Spd +5% Crit Rate +40% Hit Rate / Blind, Paralysis, Charm, Seal and Confusion Res.)
2. Void Boss: In the Void area where you meet Azazel for the first time you can also find this enemy who resembles Kageyama Shien. Collecting 50 Boss Cores from him (you can obtain an extra one stealing from Shien) you obtain the Gaming Katana (Sword, +210 Atk Dual Wielding // Void Element Gain Ability "Rainbow Break") and the Black Jackal Coat (Body Armor, +150 Def +150 Sp.Def // +20% All Element Res +25% Void Res)
3. Void Knight: After defeating Azazel for the first time, Irys give you access to the Void Forest. At the top of this area, there is a structure and near the statue there, an enemy resembling Kishido Tenma can be found. Collecting 50 Knight Cores from him (one can be stolen from his companion Hiyamaru) you obtain the Sword of Light (Sword, +250 Atk Light Element Void Element // Gain Ability "Sword of Light") and the Warrior of Light Shield ( Shield, +100 Def +100 Sp.Def // 50% Void Res. 50% Dark Res. Light Absorb)
4. Void Flower: In the same stage Void Forest, walking near the other statues, you may meet this annoying enemy that resembles Hanasaki Miyabi. Collecting 50 Flower Cores you obtain the Blooming Flower Bow (Bow, +150 Atk +90 Sp.Atk +40 Spd 50% Hit Rate Wind // Element Void Element Gain Ability "Flowering Storm Shot") and the Flower Hair Clip (Accessory, 15% Hp Regen 10% Mp Regen 10% Tp Regen // 10% Void Res. %50 Poison Res.)
5. Void Cat: After defeating Godchama, if you speak to T-chan after completing her Quiz Challenge, she will give you an item. Talk to Ao-chan and she will talk about it, unlocking a new Void area. Talk to Irys to get there. In this place, you can meet the enemy that resembles Kanade Izuru. Collecting 50 Cat Cores you obtain the Void Claws (Claw, +170 Atk +1 Attacks Thunder Element Void Element // Gain Ability "Kanade yo! Thunder Dance!") and the Black Cat Jacket (Body Armor, +150 Def +50 Spd +20% Thunder Element Res // +20% Dark Element Res +25% Void Res)
6. Void Evening: From the Void area where you meet the alter version of Izuru, if you travel to the right side of the area, you can find that there is access to another section. In that other section, there is a lone statue where you can find this enemy resembling Yuukoku Roberu. 
   Collecting 50 Evening Cores, you can obtain the Yuukoku Fan (Melee, +150 Sp.Atk +100 Lck // Gain Ability "In My Soul") and the Dusk Veil (Head Armor, +20% Evasion +20% Magic Eva. +20% Crit. Evasion // +30% Void Res.)
7. Void Android: Just before the final battle and segment of the game, when all characters are reunited on the Void, if you talk to Irys you will find out there is available a new Void area, the "Floating Ruins". Around the statue, you find on the top right of this area you can find the enemy that resembles Rikkaloid. By collecting his 50 Mechanical Cores you can obtain the pair of swords Byakko (+170 Atk 50% Barrier Penetration // Light Element Inflicts Light Debuff+) and Genbu (+170 Atk 50% Barrier Penetration // Dark Element Inflicts Dark Debuff+)
8. Void Lion: Same place as Rikka's alter, but around the top left statue, you can find the enemy that resembles Arurandeisu on his fancy new year outfit! Collecting his 50 Pizza Cores, you can obtain the Lion Mask (Head Armor, +50 Def +100 Sp.Def +100 Lck // All Basic Bad Status Resistance) and the Shishimai Cape (Accessory, +80% Magic Evasion)
9. Void Alien: Same place as Rikka's alter, but to fight the enemy that resembles Astel Leda, you have to interact with a blue orb on the bottom side of the area and offer some of the Party's Hp and Mp. By collecting the 50 Alien Cores (one extra can be stolen from Poruneu) you can obtain the Star Express Hat (Head Armor, +50 Def  +20% Void Res.) and Star Express Jacket (+70 Sp.Def +50 Lck +30% Void Res.
   +1500 Barrier // 250 Barrier Regen)