Here's what I figured out after awarding your entry to my bounty ( https://civitai.com/bounties/3700/entries/27616 ) but before you posted the Lora publicly:

1. If you prompt "helmet" and "visor" with high enough weightage, you get the helmet/visor but with eyes visible through visor, which I personally don't really mind anyway as I prefer being able to see eyes. However, you need cannot have any mentions to hair at all, or only the top half of the helmet will spawn, with the lower half of the face left uncovered to allow for hair to flow. This even includes when you avoid every hair prompt except bangs, which intuitively you would think would just show hair under the helmet above the eyes, but that does not seem to be the case. (Edit: You can get rid of eyes by adding "eyes" to negative prompt, while also including "mouth" and "hair" to prevent only parts of the helmet from spawning. I've tried adding other weird prompts as well such as "opaque visor" but they seem to do absolutely nothing)
2. If you prompt "helmet" and negative prompt "visor" then you can remove the visor, which is really cool.
3. You stated in the bounty entry that, "About putting them on bodysuit only, is kind of possible the bodysuit always retain some yellow/pink parts as if was a motorbike suit, it does not become completely black bodysuit. May be if you low the str enough is possible, but I bet then the logo on their chest will lose likeness." However, I was able to reproduce the bodysuit by removing "bodysuit under clothes, pink/yellow jacket, pink/yellow skirt, belt". But I think you figured that out too considering your sample images in this post.
4. However, it seems like if you look at their backs, the skull and cross swords symbol appears on their back, which I cannot get rid of even with all the negative prompts I've tried, which includes "skull and crossed swords, skull and crossbones, pirate, symbol, emblem, jolly roger, pirate flag, crest, logo, heraldry, print shirt, clothes writing, graphic shirt, print blouse, coat of arms". However, it does seem like if the character has long hair, the skulls and cross swords symbol doesn't appear. That doesn't really help if you want a girl with short hair though. If anyone has any insight, that would be great!
(Edit: It seems like there is a lot of RNG necessary if you are generating them from the back. The pirate symbol on their chest would randomly and spontaneously spawn on their backs (around 90% of the time), the back of their helmets (around 60% of the time), and even on their asses (around 10% of the time). Managed this by finding a good seed for the exact pose, background, etc., that I want, then varied both steps and scale, incrementing by one each, seeing the results, noting it down, and repeating, until I find a good combination that nets me what I want (i.e., no pirate symbol on their back or their helmets or their asses))
Also 5. SHIT I DIDN'T REALIZE THIS COSTUME WAS THIS FREAKING LEWD
Edit: 6. Hairbands would randomly spawn but I guess that's because Ahim wears one so it got sucked into the training data or something? Anyway, adding "hairband" to the negative prompt helps 80% of the time, further adding "hair ornament" to negative prompt helps for remaining 10%, and for the last 10%, I would try to increase weight on hair color or give up and find a different seed

just a bit of feedback too, Pink and yellow helmet are different in design, sometimes you get pink helmet on yellow, and yellow helmet on pink. this kind of loras are better as separated characters