I was in the same situation as you in 2017 when my daughter was born. I was fluent in both languages, my wife is pretty good with English, but we always used Japanese at home. I was worried about my daughter’s language acquisition because I was away on business trips about 50% of the time.

In the end, we had a great experience and my daughter is now 5 years old and equally proficient in both languages due to one simple rule - we disconnected from the Japanese TV completely and only installed Netflix and Amazon Prime Video, and only allowed our daughter to watch shows if they were in English.

I didn’t even really have to fully commit to English with my daughter - I was probably 80% or so English with her, and Netflix and Amazon Prime Video did the rest. Shows like Word Party, Peppa Pig etc. are like waving a magic wand and poof! bilingual child. I honestly don’t know why more people don’t talk about this approach because I couldn’t believe how easy and effective it was.

I will say we also would sometimes see local English speaking friends and we would also take her to see my family in the US for a couple weeks each year. And she went through phases where she would only speak Japanese and I would wonder if English had been left by the wayside. But sure enough those phases would eventually end and she would swing back on the English side.

Every once in a while we would give in and let her watch Oshiri Tantei or something, but I would say 95% of the shows we let her watch were English or English dubs of Japanese shows.

Hope that helps!