Do I need to establish LLC in the US when we launch an app in App store in the US

No, but from memory (I did it over 10 years ago) you will need to create a US tax file number or whatever they call it there. the iTunes connect process will take you through the process (or at least it used to).

I think you also need one for Japan and one other country (Canada?) from memory if u want to avoid withholding taxes for sales in those locations.

not sure if the process has changed now. feel free to correct me if it has.

Are there specific rules for dating apps?

Otherwise - no, you don't need a US LLC. You just need the US taxpayer number. This looks a bit intimidating but it's not difficult. The most challenging part is spelling your foreign address over the phone. Get a "NATO Phonetic Alphabet" on the screen before you start! The person I dealt with was very friendly. Have you ever been though US customs/immigration? - it's the exact opposite experience. When the US govt recruits people, if they are arseholes they send them to immigration, and if they are lovely they send them to the foreign tax registration helpline.

There used to be something odd about tax in Japan but I think that has gone.

Thank you for the answers! 

I did further research and it seems like the U.S. taxpayer identification number (TIN), I think this is what you meant?, is not required as long as we are not living in the US and does not have any business entity in the US.

They asked from apple finance team and IRS dealing with TIN. 

Here are sources. 

https://discussions.apple.com/thread/3105682

https://developer.apple.com/forums/thread/660025

You do need a TIN.

It's not difficult.