This is one of the best stand alone books for Word of Darkness. Few WoD supplements can stand on their own but Demon Hunter X does an excellent job of telling you everything you need to start playing as Shih or Agent of Strike Force Zero in Japan, if you already know the story teller system really almost no other books needed (though Kindred of the East will probably be very helpful for Storytellers).
This books strikes an excellent balance between giving you RP flavor of Demon Hunter X, mechanical information like new powers and abilities and storyline ideas for the series. Further the book is extremely well written and with rules and concepts being clear and easy to understand even for those not familiar with the WoD:East material. Demon Hunter X certainly has a different flavor than most Word of Darkness lines being more anime influence, but it comes off as refreshing and still in line with the spirit of World of Darkness as whole. Finally Demon Hunter X does a good job establishing Japan, an area rarely explored in most other WoD material and bringing it to life in spite of a limited page count. DHX is one of my favorite World of Darkness supplements.
*Note: WoD: Tokyo does also explore Japan but is a Wraith Supplement so while it touched on all WoD lines it isn't tightly focused, not necessary but like Kindred of the East can be a good supplement to DHX to help round out the DHX setting and expand on some WoD:East concepts.