Hello, friendly advice from a fem-presenting UK person who loves writing.
It feels like you still don't have a very clear idea of what this project actually is, but rather it's a mashup of tropes and staple arcs from your favorite manga and anime, which has lead to something that is way too big in scope and muddled in tone and focus. This is how Sword Art Online's first series came to be the hot mess they were writing wise.
You say you have strong pacing, foreshadowing and all, but you also say that everything - including plot beats and character arcs - is flexible. These two statements aren't compatible. Plus, you say you're looking for someone to write dialogue and slow burn romance and all, but I'm not sure there'll even be time on the page to develop any of that with how you'll find a way to justify a prison break arc, a tournament arc, detective arc, horror arc, etc... (again, it's giving SAO season 1 where it tone shifts every two episodes so you don't have the time to really get bored of the bad writing in any singular storyline because maybe you'll like the next genre more. Also, again, SAO is not valued for it's writing quality, in part because it's trying to do too many things at once and none of them are very good).
Regarding looking for a woman... I see you've fallen into believing the stereotype that women inherently know how to write relationships better than men. That is not the case; like all writers is especially true when writing relationship dynamics the writer is not personnally experienced in. For example, if your female writer has few male friends, she will have a bit more difficulty writing things like dialogue between men in exclusively male spaces (i.e. stuff like locker room talk, segregated dormatories, etc...). For example I have very little experience of heterosexual men my age, so I don't tend to write them, so I don't think I would be a good fit for your story despite fitting many other criteria. There are more justified reasons that people seek out female co-writers, but it's for more specific experiences linked to womanhood, such as growing up experiencing sexism, helping to write female characters in male-dominated roles or often misrepresented situations, or in stories dealing with specific types of violence, etc... The one thing basically everyone on earth will have some experience with is "relationships to others".
So, word to the wise: the combination of not only specifying that you're looking for a female co-writer for stereotypical and non-specific needs, added to the fact that you're looking for someone young between specific ages, and that live within reasonable travel distance to you, it does still throw up some... orange flags let's say. Not only does it kind of insult male writers, insinuating that they can't write any relationships, including platonic friendships within the "crew", but it also kind of sounds a bit like you're looking for a date as well as a co-writer. I'm not saying that's 100% your intention but that is how it reads to me, your "target" audience.
TL;DR: the pitch needs work, still seems way too unfocused and like a collage of cliché shounen you like and you don't seem very attached to any defining factor in the story if someone else can just come in and change everything. Plus the woman specific part may be offputting to the people you're trying to attract.
As it's your passion project, I really think it would be better for you to use that passion to give it another year or so working on it by yourself to get it to a more polished place, even start writing a few episodes in novel form and commissionning specific chapter illustrations at first because that'll be way more accessible to you and gives you a stable work pace and proving ground. Many manga start as lightnovels in this format, with chapter illustrations and the like, and though lightnovels are often panned for bad writing, this is a product of them being rushed; you don't have deadlines, so you don't have to rush. You can also use the opportunity to practice your dialogue writing and get critique to improve on the flaws you've identified in your work. Having a strong, specific pitch with a story that isn't just built on tropes will also help hype potential future co-writers up, which will help you find one.
