In case people are curious on how to get the rest of the costumes, I'll list my full experience on getting them on my own run with a more comprehensive guide on it;
Slave Attire: (Passive: Allows strength to push larger boulders, double endurance, zero defense)
1. Can be acquired from a Witch in the Forest Entrance; this must be done before finishing the Fortress Stage provided you did not defeat the Chancellor yet. You can access the Forest Entrance early by finding the hidden path that is hidden behind a tree in the Intersection Road that connects the Lone Hut, Desert Village, Mountain Pass and Dolto Village.
2. If you finished the Fortress Stage upon defeating the Chancellor and missed the opportunity, you are provided with an alternative by find the Slave bum in Gald Castle Town at the front of the Adventurer's Guild. Provide him the Canned Herrings and he will ask for better clothes. You can acquire the said clothes from the Gald Castle Town's Equipment Shop. You'll need at least a total of 55k gold total; 30k for the Free Pass and 25k for the attire.
Ninja Attire: (Passive: Allows water walk and lip reading, agility focused and evasion tanking, below adequate defense, specialized use of shurikens turning into multi-hits. Wind Attribute.)
- The Ninja attire is impossible to miss. You can find it in a blue chest in Dolto Town, east.
Maid Attire: (Passive: Allows access to a room in Gald Castle Town, high defense and physical attribute resistant. Flame Attribute.)
- There's a quest in the Gald Castle Town Tavern, the bartender on the left will ask you to deliver a hot meal to a guard that left early for duty. The right guard you're looking for is one with the given hint of 'Fancy Boots', it's a guard with blue shoes. The guard is located down southwest.
Sister Attire: (Passive: Disguise as one of the sisters, high defense and magic oriented offensive, provides resistance to poison and ice, relatively low physical power. Ice Attribute.)
1. This attire can be acquired for free by speaking to Kate in the second floor of the Church.
2. Provided that you did not speak to Kate before she turns infected if you did not investigate the underground of the Church, you can acquire the attire from a bunny girl in one of the residence down below of the Castle Town.
Samurai Attire: (Passive: Keen perception in allowing discerning details that wouldn't be noticeable, physical auto-counter and resistant, High power and critical rate, adequate defense. Electric Attribute.)
- Upon defeating the Yamigato(?) Assassin, Doppelganger and saving Ann Suu from the Forest, the Seal Case will allow you to visit the Hidden Village, unlocking it's destination. Speak through the Blind Monk and acquire information regarding the town and then speak to Tokimure in willingness to take the quest in investigating the sealed cave. Finishing the questline through and through will award you the attire.
Naked King/Invisible Armor for Fools Attire: (Passive: Nada, just pure exhibitionism. Consumes 10 SP for each attack evaded with 85% natural evasion, all attacks are performed double and negative defense. N/a Attribute.)
- Speak with the Knight of Rose Emissary at Dolto Village that stands in front of the travel board. He will guide you to speak with the Town's Storage Watchman and issue the password. (Don't worry about typing the password, speak to the Emissary again regarding to change to choices and you can select the password informed instead.) Finish the Resistance Tunnel stage as well as the Randora Caverns, there will be an old man at the right handside of Gald Castle Town, speak to him and provide him the following items; Kebab Sandwich, Exquisite Cheese, Miso Soup, and lastly Buttered Potato to acquire the Attire.
> Kebab Sandwich can be acquired from the Desert Village Sinado from the one shopkeep.
> Exquisite Cheese can be acquired from quests or dungeons; there should be enough excess in case you turned them in for quests.
> Miso Soup can be acquired from the Hidden Village's shopkeep.
> Buttered Potato can be acquired from the General Store clerk in Dolto Village.
Sage Attire: (Passive: (Have not figured out yet), increases physical and magic offensive powers but also increases damage taken the same return. Decreases 10 SP each turn. Universal Attribute(?))
- The Attire is acquired by doing all the available and subsequent quests provided by the Adventurer's Guild in both Dolto Village and Gald Castle Town. (The three quests outside the Guild are excluded as they are repeatables). Speak with the guild master after submission of the final quest.
WARNING: If it is your first and single run, using the Death Stone to smith into a weapon makes the attire unattainable. (Provided there is a way to acquire more Death Stones that I do not have knowledge of yet.)
Cyber Attire (Cecilia E.): (Passive: (Have not figured out yet), mitigates damage taken, electric resistant, auto SP recover and significant critical hit rate increase, at the cost of HP drain over turn.)
- Finish Cecilia E.'s main task from the beginning of the game and return to hosting Cecilia. (Basically just finish the main story and beat [REDACTED] boss while you help Cecilia.)
If there's any discrepancy, feel free to question and I'll try my best to discern possible issues. Meanwhile, regarding allies you can recruit, I have not unlocked all of them and only have access to two, that is to say you can only have two to choose from. Will come back and post about it if there's any more.