The overall sad tone of the song, it had this ominous and murky feel to it that brought deep emotion in the track, and it fit the stage really well. It's one of my favorite tekken themes
It's quite upbeat, it indeed is a pretty cool track, but i never found it sad.
Jann Lee's DOA4 ending theme (which i recently found out is called, “The Fist”) is a pretty deep track, Brad's DOA3 ending theme (Perpetual Motion) is an extremely powerful song, that ending is already beautiful as it is, but that song makes it about about a thousand times better.