You can simply come on visa exemption and get 30 days permission to stay. After that, you can get an extension for 30 days inside Thailand at any immigration office. However, some airlines and immigration may ask to see a return or onward ticket within the 30 days permission to stay granted by your visa exempt entry. Therefore, you can chance it and hope you don't get asked or buy a cheap throw away ticket to Cambodia for example to show if you are asked to show a return or onward ticket within the first 30 days and then use your real return ticket later. I don't recommend using one of those websites that will sell you a reservation for the return flight within 30 days, as the Thai government is getting wise to that. However, that would be another option, just not the one I would recommend. Hope this helps.
Inheritance tax is also ridiculous here. There's a 36 million yen exemption, and then after that a horrific sliding scale whereby the more you leave behind, the more they screw you. The maximum rate is over 50%.
Basically, taxes in Japan are very low when you're alive, but then they really nail you when you're dead.