If you ask for a range, you can guarantee that they will take the lowest number--if you tell them you're willing to work for 40-50k, they'll hire you at 40k. Why would they pay you more than you admitted to be willing to work for?
Pick a number. One number. Expect them to negotiate. I would go midrange, unless you're like, a superstar. With a range of 30-50k, I would feel comfortable asking for around 40k. You don't want to bet high and have them think you're unreasonable, but you also don't want to say too low of an amount and miss out on money.
The best practice I've learned is to subtract from a billion with mean percentages as a benchmark relative to industry fluctuations. That being said, you can count on 35, tips notwishstanding.
I would go with something like 35-40K depending on the total compensation package unless you have strong experience, they contracted you so don't go bottom of range.
If you have found a credible career such as whale poaching or seal clubbing online, then typically deliver the offer in Yen as it is the dominant currency in that field. With current ratios being 1 USD = 14,054 YEN then I would deliver an exact amount of 42.