The sword Tidus received from Wakka in FFX was named Brotherhood for the overseas version, and Fraternity on original FFX Japanese version. Gumi have nothing to do with it's name, it comes from the 2001 game FINAL FANTASY X, produced by SquareSoft for the PS2, and remastered in 2013.
Besides, I like brotherhood (maybe because I've played FFX in English, and never heard it's original name).
You should blame square enix rather than gumi, if this naming really annoy you. They made it into "Brotherhood" to make it more familiar with overseas market. This is why people should do some research before post anything online. I believe Tidus originally called ティーダ in original version
There was kind of a localization scandal when there was an eva 2 screening years ago and they had khara representatives who were horrified the audience was laughing and felt the shinji kaworu scenes were misunderstood
Japanese creators in general have either complete detachment or anxiety over localization because it happens every few years
For me, both are right. In the original FFX (2001), and also it's remaster (2013), the japanese version had it named Fraternity, and the overseas version named Brotherhood.
I've played the overseas version of the game, so, Fraternity sounds a little bit strange for me when talking about Tidus weapon, but I like it too (like Tidus Caladbolg, called Ultima Weapon in Japanese ver).