Otoko Ippiki Gurren Lagann (男一匹グレンラガン Otoko Ippiki Guren Ragan) is the first in what would ultimately be a trilogy of drama CDs for the Tengen Toppa Gurren Lagann series. Otoko Ippiki Gurren Lagann was released in Japan as a bonus feature of the Tengen Toppa Gurren Lagann Volume 5 DVD.
The Drama CD begins with Leeron announcing how this Drama CD has nothing to do with the original Tengen Toppa Gurren Lagann, or "Beastmen-chan, Team Gurren-chan, Spiral races-chan, or Anti-Spirals-chan", before kissing us off to the main storyline.
A local roughneck, Kamino Kamina, introduces himself to a pair of yakuza from the Ginbu Clan (after beating them up). Kamina then dramatically announces the title (he then remarks that there was a theme song, but because of budget and time, it was cut; "play theme song in your souls!"). He then arrives late to class in Dai-Gurren Academy, and his childhood friend Utsuwa Yoko, remarks that it's odd for him to show up to school in the morning. He then begins studying for that day's test; if he fails it, he will have to repeat the year. Kamina tells Yoko that he's working to graduate because his deceased father told him to. It's a shame that they're not having an English test (Kamina's reading the English textbook); Yoko reminds him that it's the physics test today.
A motorcycle revs outside, freaking out fellow classmate Awa Tensuke; it's Kamina's rival from Bachika High, Kurono Kitan; Kitan has arrived to show Kamina who the toughest in the city is. Kamina bolts off to fight him, but is impeded by the board chairman, a young American girl named Nia, who cautions him not to run in the halls, her piggish-molish pet Buuta, and by Hotta Shimon, who is himself the entirety of Dai-Gurren Academy's Maintenance Department. A pipe bursts nearby, and Nia coaxes Kamina into aiding Shimon in fixing it. Outside, Kitan continues to call Kamina's name, and is accosted and dragged off by mystery assailants.
That evening, Daya Kaizou excuses Kamina for missing his physics test, by virtue of his aiding Nia and Shimon fix up the broken pipe (Shimon was amazed by Kamina's being able to tear out the floorboards faster than his drill). Of course, Rino Ronta, his physics sensei, tells him to do a report in place of the test. Outside of Dai-Gurren Academy's gates, he and Yoko are accosted by three sisters, Kurono Kiyou, Kurono Kinon, and Kurono Kiyaru, who accuse Kamina of doing something to their big brother, Kitan. Yoko finds a Ginbu Clan mark on the ground where Kitan was yelling before, and Kitan's sisters realise their brother was kidnapped by yakuza.
In a mystery facility, Kitan is tied to a chair. Ginbu Rei asks Ohba Jougan and Ohba "Barinbou" Rinbou why they brought him a man who was not Kamina. They explain that he was shouting "Kamina!", so they thought it was him. Ginbu-san yells at them for being so idiotic, and Viral Sassoon, an agent from the American organisation known as the Teppelin Foundation, joins in after a while. Evidently, Viral gave them the order to kidnap Kamina. Kamina bursts in through the window, having seen Kitan's motorcycle outside (Jougan and Barinbou did not hide it, deciding to worry about it later) and then leaps back out with Kitan. They land on an air cushion Kitan's sisters had gotten off of a fire truck. Yoko helps to ride Kamina to his home on her motorcycle (Kitan and his sisters follow on his bike, the King Kitan). The Ginbu Clan pursue, but fall down a pitfall dug out by Shimon.
At Kamina's house, Ginbu Clan members arrive mere moments after their arrival, and open fire on Kamina's home. Rino-sensei contacts Kamina via cell phone, telling him to go behind his father's bookcase to find his father's legacy. Back at the Dai-Gurren Academy, Rino-sensei and Daya-sensei meet with Nia and Shimon; apparently, they are mobilising in preparation for a Teppelin Foundation attack. Behind his father's bookcase, Kamina finds a locked door, and a computer asking him to insert his soul; he punches it, which it accepts, opening the door. He is amazed at what's behind it.
Outside, the Ginbu Clan are shocked as a part of Kamina's house collapses, and a large red robot with sunglasses emerges. Ginbu-san orders Zorthy and Kid the Quick to open fire, but their weapons do nothing. The robot is the legacy of Kamina's father Professor Kamino, Gurren. He tosses their cars away, and Yoko and the Kurono siblings are called away by Rino-sensei to Dai-Gurren Academy. Elsewhere, Viral meets with Rossiu Dekoi, pokes fun at Rossiu's punny surname (deko is the Japanese word for forehead, and Rossiu's is quite large), and asks if his Enki in the nearby trailer is on standby.
As Ginbu-san warns his men not to run from Gurren, a white Gunmen approaches, and the Ginbu Clan men run away. The white Gunmen is Enki, piloted by Viral. Enki beats Gurren down, and Kamina is suddenly contacted by Shimon to combine with his own Gunmen, Lagann (built by Shimon's father, Professor Hotta). After more attacks from Enki, background information from Nia, and prodding from Yoko, Kamina agrees to a combining, telling Shimon to call him Aniki. Lagann's drill nearly pierces Kamina's head, but he ignores it as Gurren and Lagann perform a "Brotherly Combining" into Gurren Lagann, which deflects Enki's missiles with a Giga Drill Maximum.
Sensing that the battle is turning against him, Rossiu launches the Dai-Gunkai. At Dai-Gurren Academy, Yoko and the Kurono siblings learn that Daya-sensei and Rino-sensei are comrades of Nia's in a battle against the Teppelin Foundation, just before the Dai-Gurren itself is launched (Shimon laments having to do massive repairs to the school). Dai-Gurren's weapons batteries (operated by Yoko) take out Dai-Gunkai in one shot, and Gurren Lagann uses a Giga Drill Break straight through Enki. Viral vows to be back.
Nia reveals her full name as Nia Teppelin, and that she is the daughter of the president of the Teppelin Foundation, who left America when she learned of her father's plans to forcibly take control of Japan. She then commissioned Professors Kamino and Hotta to create counter-Gunmen to oppose the Teppelin Foundation's Gunmen. Kamina vows to be there waiting for them with Otoko Ippiki Gurren Lagann. Shimon asks what Kamina means by that; Kamina explains that Shimon isn't yet fit for 'hitori' (in other words, 'a man'), so 'ippiki' is enough. Kamina explains that he himself is the 'otoko' (man) of Otoko Ippiki Gurren Lagann, and that Shimon is the 'ippiki'. Shimon is upset about the nature of the subtitle.
Later, Rossiu attacks with a fortress Gunmen known as the Dai-Gunzanten, and Viral attacks with a hundred Enki Gunmen. The one with two arms is called Enkidu, the one with four arms is called Enkidudu, the one with six arms is called Enkidududu, the one with eight arms is called Enkidudududu, a rooster's crow is pronounced cock-a-doodle-doo, and the call to stop a horse is doh-doh (at which point Viral loses his cool at such ridiculous dialogue). The Drama CD ends on a cliffhanger that is not (directly) resolved.
Kamina gives a Next Episode Preview for Otoko Ippiki Gurren Lagann: Conclusion Chapter!: "Gurren Lagann's great pinch! Rossiu's forehead gleams with killing intent!", telling the listener to look forward to it.
- Kamino Kamina (神野 神名) - A roughneck in Dai-Gurren Academy, Kamina lives by himself, his mother having died when he was young, and his father the year before in a car accident. His father was a scientist who worked for the Teppelin Foundation. He pilots Gurren, the Gunmen his father constructed to oppose the Teppelin Foundation.
- Hotta Shimon (堀田 志門) - The Maintenance Department in Dai-Gurren Academy. His father was a scientist who worked in the Teppelin Foundation. He pilots Lagann, which can combine with Kamina's Gurren to become Gurren Lagann.
- Utsuwa Yoko (宇津和 庸子) - The president of Dai-Gurren Academy's Newspaper Club, Dai-Gurren Academy's Motorcycle Club, Dai-Gurren Academy's Air Rifle Club, Dai-Gurren Academy's Long-Range Bombarding Club, etc. She is Kamina's childhood friend, and becomes the main gunner of the Dai-Gurren once it launches.
- Nia Teppelin (ニア・テッペリン) - The board chairman of Dai-Gurren Academy, and daughter of the president of the Teppelin Foundation. When she learned of her father's ambitions for conquering Japan, she left America and fled to Japan with Professor Kamino, Professor Hotta, Dayakka and Leeron. Dai-Gurren Academy was set up to oppose the Teppelin Foundation.
- Buuta (月ー豕) - Nia's pet, which no one can tell if it's a pig or a mole.
- Kurono Kitan (黒野 騎丹) - A roughneck from Bachika High, and Kamina's rival. His motorcycle is named the King Kitan.
- Kurono Kiyou (黒野 キヨウ) - Kitan's eldest younger sister. Her weapon is a metal paper crane.
- Kurono Kinon (黒野 キノン) - Kitan's middle younger sister. She becomes the radar operator of Dai-Gurren (even though she attends Bachika High). Her weapon is a Lilian knitting needle.
- Kurono Kiyaru (黒野 キヤル) - Kitan's youngest sister. She speaks roughly, a sign of her big brother's influence. Her weapon is a yo-yo.
- Viral Sassoon (ヴィラル・サスーン) - A Teppelin Foundation agent. He places a lot of concern on his hair. He pilots the Gunmen Enki (and the Hundred Enki Forces).
- Rossiu Dekoi (ロシウ・デコイ) - A high-ranking Teppelin Foundation agent. He is often the brunt of jokes about his forehead and unfortunate surname by Viral. He pilots the Dai-Gunkai (then the Dai-Gunzanten) in Otoko Ippiki Gurren Lagann.
- Daya Kaizou (打屋 海蔵) - A sensei at Dai-Gurren Academy. He was originally named Dayakka in the States, when he worked for the Teppelin Foundation, but goes by the alias Daya Kaizou while undercover in Japan.
- Rino Ronta (理野 論太) - The physics sensei at Dai-Gurren Academy. His name was originally Leeron while living in America, but when he left the Teppelin Foundation with Dayakka and Professors Kamino and Hotta, he changed his name to Rino Ronta (although he is rather loose with this, referring to Daya-sensei as Dayakka).
- Ginbu Rei (銀部 礼) - The current head of the yakuza group known as the Ginbu Clan.
- Ohba Jougan and Ohba "Barinbou" Rinbou (大場 丈岩 and 大場 林望) - A bumbling pair of twins who serve under Ginbu Rei.
- Kid The Quick (キッド・ザ・クイック) - A gunman hired by the Ginbu Clan.
- Zorthy (ゾーシィ) - A fellow gunman hired by the Ginbu Clan.
- Awa Tensuke (阿波 天助) - a classmate of Kamina and Yoko's.
- Otoko Ippiki Gurren Lagann gets its name from a 1968 manga and 1969 anime series: Otoko Ippiki Gaki Daishō (男一匹ガキ大将, meaning Otoko Ippiki Boss of the Kids).
- Viral's full name is a pun on Vidal Sassoon. Appropriately, he has a lot of pride in his hair.
- Rossiu's surname is a pun on the Japanese word for forehead, deko. Rossiu's forehead is the brunt of several jokes in the Otoko Series.