It is recommended that you be at least level 60 and have a Longsword Skill/Greatsword Skill/Dagger Skill of level 6+. The Lightning Wraith has a lot of health and high damage so challenging it early on in the game won't work; it's just going to kill you. Make sure to stock up on Life Cures and Potions! If you can lure it into the corner you can combo it with tornado spin infinitely.
If you're a Magician or Hunter, you can probably take it on underleveled if you know what you're doing. Stock up on life cures and HP/SP recovering items just in case, and once you're fighting it, open up with an X-charged attack, since it won't attack you until you attack it. After that, switch tactics to firing one attack at it, moving about a third of a circle around it, fire another shot, maybe two if you feel confident, repeat.