See Tachi: Enpi for the translation of "Tachi:" The original weaponskill from the Japanese version is: 参之太刀・轟天 (San no Tachi: Gouten) "Third style of the tachi: Roaring Heavens" (轟 is roaring, thunderous, and resounding. And 天 is the sky and heavens.) Goten seems to refer to a type of battlecry, or a summoning of inner strength. Samurai utilize STR for power, and Lightning tends to be the most powerful element in FFXI. Taking that very loose description, you could associate the weaponskill's effect of Lightning damage, and STR modifier, to draw a connection.