Just like NA forum the JP forum is asking why is the repair item Dark Matter? they feel that Dark Matter is unknown element in previous FF series and doesn't match as a repair item. Also Dark Matter being some item you get towards end of the game in other FF series, why is it going to be a common item in FF14?

Original Thread Link: http://forum.square-enix.com/ffxiv/threads/16464

Quote Originally Posted by Mocchi View Post
こんにちは。
Hello,

「修理材料の名称がなぜダークマターになったのか？」について開発チームと話をしてきました。
Talked to the dev team on why "repair item was named dark matter"?

エオルゼアにおいて、どんな装備品でも修理可能な修理材料はとてもとても重要な物質であり、今後もずっと使用され続ける存在のため、ダークマターという名称を用いることになりました。
It was named Dark Matter as it is a very important material that can repair any type of weapon/gear and will be continues to be used in the world of Eorzea

そして、「ダークマター」や「属性を失ったクリスタル」が採れるようになったという事実は、エオルゼアに訪れる激変の予兆だと言えるかもしれません。
It may be it is a sign that major changes are coming to Eorzea since "Dark Matter" and "Deaspected Crystals" can now be obtained.
pretty sure NA rep will translate this one and post official one, but that's it means in the JP rep response version.