Well, ladies and gentleman, it has happened, hell has frozen over, pigs have started flying, the steps to bring down the horrible, HORRIBLE company that is SoftBank has started.
Thanks to our friends at U-Mobile, if you have a phone that is locked to SoftBank (actually, if you don't mind, I will refer to them as S**tbank, which actually just censors the "o" and "f" but looks like the word we really think of when we think of S**tbank), you can take advantage of their new SIM (https://umobile.jp/service/s/), which uses their network but not at rates like ¥410938472439582349x10 per day, which is S**tBanks minimum fee for a single SMS sent domestically in Japan.
You may have noticed in the adverts on the trains that S**tBank has started their own MVNO, which the aim for casual users. However, Son-san (S**tBank's CEO and, completely coincidentally, a close pal of Donald Trump) is so obsessed with cash to a pathological level, that they've priced this MVNO at about ¥2000 more than the nearest competitor. Oh, S**tBank, when WILL you ever learn? (Spoiler: Never).
So, my advice? Get on Craigslist or go to Janpara/SofMap, buy a 中古SoftBank iPhone 7, which will be cheaper than an unlocked model, get a U-mobile SIM and then go to the massive SoftBank HQ and duly give that POS company the finger they so truly deserve to have as their logo mark