"Where There Is Light, Shadows Lurk And Fear Reigns. Yet By The Blade Of Knights...Mankind, Was Given Hope."
"Garo (牙狼〈GARO〉（ガロ）, "Fanged Wolf"), sometimes referred to as Golden Knight Garo (黄金騎士ガロ Ōgon Kishi Garo), is a Japanese tokusatsu television series broadcast on TV Tokyo from October 7, 2005, to March 31, 2006, lasting 25 episodes (with one additional "Overview" special, summarizing the events of episodes 1 through 13, aired before episode 14). Since 2007, the show has also been aired in other countries such as Italy (on MTV), Malaysia (on 8TV), and Spain (on Canal Buzz). The show's HD remastered version was broadcast on TV Tokyo starting July 8, 2016. The television series is the first installment of the "GARO" franchise, which is composed of several installments, including a live action television series, films, TV & film specials, and anime series. The television series has been licensed for a North American release by Kraken Releasing." - Wikipedia
"Since the beginning, the darkness within humanity had the power to influence the spiritual makai realm. It is through this darkness which creates malevolent creatures called Horrors, a destructive spiritual predator that breaks into the human realm through gateways. These gateways are also influenced through dark energies, be it a gun or a lamp, if the object or place is contaminated with enough dark energies, it becomes a crack between realms that allows Horrors to escape into the human realm, where the Horror(s) can cross over and posses and/or prey on humanity as subsistence. As creatures that operate within the shadow, many lives were ruined and destroyed by the Horrors; they aim to turn the world into darkness. The only force preventing their attempts to overthrow humanity is the Makai Order. Through use of spell-casting, mysticism, and martial arts, the Makai Order established their own shadow force of priests and knights that secretly hunt down and defeat all forces of darkness. One such defender is the Makai Knight, Golden Knight Garo." - The GARO Wiki
In MAKAI REVIEWS, yours truly will review the entire GARO series, every installment and film, episode-by-episode, special-by-special.
Taka The anime is...kind of a bad entry point to the franchise if you're not already familiar with the tokusatsu genre. The feel, and especially the action in the anime is not in line with the source material at all. Someone who got used to seeing the characters dashing miles in seconds, jumping hundreds of metres into the air, blasting massive amounts of energy, and taking down huge monsters, and all of those shonen action mainstays might be disappointed when they see that the actual GARO series' action is far more grounded.
It's centered on the Wuxia film variety of action (Crouching Tiger - Hidden Dragon, Heavenly Kingdom, House of Flying Daggers, etc.), focusing on martial arts, great choreography, and special effects (both CG and practical) to add he fantastical element to the combat scenes (though I've heard that the series diverges from this style by the 3rd installment, unfortunately).
But on the other hand, it does give you an idea about core concepts like Makai Knights, Horrors, and what have you, but I still think it's not a good gateway to the live-action counterpart.