|This article is about a/an episode in Juken Sentai Gekiranger.|
First Lesson: Niki-Niki! Fierce Beast-Fist (修行その１ ニキニキ！激獣拳 Shugyō sono Ichi: Niki-Niki! Geki Jūken) is the first episode of Juken Sentai Gekiranger.
On a lunar eclipse that occurs every 500 years, the Kenma Bracelet must be sealed at an area surrounding the Beast Fist Life Tree, so it would be out of evil's hands forever. But, Fierce Beast Leopard-Fist user Miki Masaki encounters a wild child named Jan Kandou before she is attacked by a group of Akugata Rinshi led by Confrontation Beast Mantis-Fist user Makirika, who steals the Bracelet. Then, the leader of Confrontation Beast Hall, Rio, obeying the souls of the long dead founders of the Rin Jūken style, starts their plans to conquer the world by first amassing Rinki energy from the terror inflicted on humans.
However, the Grand Master of the Fierce Beast-Fist style, Fist Sage Sha-Fu, along with Miki have been prepared for this coming battle and were training two young fighters: Fierce Beast Cheetah-Fist practitioner Ran Uzaki and Geki Jū Jaguar-Ken user Retsu Fukami. Jan joins the other two warriors in forming the Gekiranger team. However, they face Makirika, now a Beast-Man after absorbing enough Rinki. Though Jan manages to defeat Makirika with his newly-developed Fierce Beast Tiger-Fist, the Beast-Man soon grows into a giant.
- As part of Super Hero Time, this episode aired alongside Kamen Rider Den-O episode 4, Get Out, Oni! I am Serious
- Pre-Ending: Miki explains Geki and the Beast-Fist Transformation GekiChangers
- If you watch closely with the explanation of Geki, you see several animals that will become notable later, including an elephant, gorilla, rhinoceros, penguin and gazelle.
Juken Sentai Gekiranger Volume 1 features episodes 1-4: Lesson 1: Niki-Niki! Fierce Beast-Fist, Lesson 2: Waki-Waki! Beast-Fist Combination, Lesson 3: Shio-Shio! Cleaning Power, and Lesson 4: Zowa-Zowa! The Five Venom Fists. 
- Welcome to the Jungle - Power Rangers counterpart in Power Rangers Jungle Fury. See comparison page.