Anybody here has the situation as mine, I am a half Japanese and mom wants to apply my visa as a Child of Japanese National

I am 23 years old and my mother is Filipina living in Japan (Long term resident only) and my dad is a Japanese citizen who is bedridden. Mom wants to hire a lawyer to process my visa for the "Child of Japanese National" but the thing is I am an illegitimate child and I am not in the koseki tohon or family registry, and I know that my father's legal wife and family won't accept that I want to go in their family registry. anyone have the same situation as mine? Any tips or advice. Thank you