Right...this is starting to look like it needs a proper reality check...
So, the only way this will work is if you are a fluent speaker and writer of Japanese. If you're not, you should drop this idea right now.
My understanding of the Japanese light novel industry is that they will often source new authors and series from web novel sites. These are NOT light novels yet. They become light novels once they get picked up by a Japanese publisher, at which point they are rewritten in the light novel format with the help of a professional editor (so, for example, there are significant differences between the Rising of the Shield Hero web novel and the Rising of the Shield Hero light novel).
The people who work in Japanese media generally are not fluent in English. If you want to deal with them, you have to do it in Japanese. So, the only way that you can get a light novel published in Japan is to have something that reads well in Japanese, and to be able to speak and read the language well enough to get through the contract negotiations, if they are interested at all in the first place (and that interest might disappear as soon as they find out that your Japanese pen name is nothing more than a front).
Then there's the problem of translation. I've done translations from French and German in English. It's not easy. Even with translation software, you have to spend weeks fine tuning the English text into something good and readable. My translation of the first volume of Joffre's Memoirs took almost two months. So, the only way you're going to turn an English text into a Japanese text is with the help of somebody who is fluent in that language cleaning up the translation.
(And I can speak from experience on that too. For the planned third volume of Re:Apotheosis, I'm hoping to get permission to use a character from Re:Creators. So, I contacted Troyca to ask if it was possible to get permission. The language I had to use to get Google translate to go back and forth between languages and keep the same basic meaning was simple to the point of being bad writing. There is no world in which this could work for fiction.)
If you want to break into the Japanese light novel market without being fluent in Japanese, I'm afraid the only way I see it working is to write a good book in your native language as yourself, and be successful enough that a Japanese publisher hears about it and contacts you to get the translation rights.