Koji is tall, and has a large muscular build. His head has the form of a rock, which is unevenly shaped and pointed at the top of his head, and his jaw is square shaped. His skin is peach colored.
Koji is a very shy and quiet person, as such he rarely speaks and prefers using sign language to communicate with his classmates. According to Fumikage Tokoyami, he is very good at keeping secrets.
Koji suffers from Entomophobia, being deathly afraid of bugs, with the mere sight of them making him scream and run away in fear. However, Koji is capable of (reluctantly) putting this fear aside if it means helping his comrades.
Koji places 20th in the Obstacle Race, allowing him to participate in the next event, the Human Cavalry Game. He then teams up with Tooru, Kyoka, and Rikido. Koji fails to advance to the tournament event due to his team being unable to accumulate enough points to advance.
Koji along with his class watches the closing ceremony of U.A.'s Sports Festival.
Two days after the Sports Festival, Koji is in class. During the Hero Informatics period where the class has to decide on potential Hero names, Koji writes down and shows his Hero name: Petting Hero Anima (ふれあいヒーロー アニマ Fureai Hīrō Anima?).
After Class 1-A is finished formulating their Hero names, Koji is given a list of 40 work places in order to choose a work place that he wants to train at. On the day of the work place training, Koji is at the train station with his class so that he can travel to the work place of his choice by train.
Koji is paired with Kyoka and they must face Present Mic within 30 minutes in order to win and pass the test. The test begins.
Present Mic uses his loud voice to keep Kyoka and Koji off guard. Annoyed by Present Mic's loud voice, Kyoka tells Koji to command the nearby animals to attack, but Koji is unable to due to Present Mic's voice making the animals wild and as a result, any command he gave would be useless.
Kyoka and Koji manage to get a little closer to the escape gate, but Kyoka notes that Present Mic will be at the escape gate and that no matter what option of victory they choose, a standoff is inevitable. Present Mic uses his loud voice again; Kyoka notes that they cannot get any closer as long as Present Mic is using his Quirk. Kyoka sees an ant and comes up with an idea; she asks Koji if he can control bugs, but his terrified reaction indicates that he doesn't like bugs. Present Mic uses his loud voice once again; Kyoka tries to counteract with her Earphone Jacks' but the sound of her heartbeat doesn't do anything against Present Mic. Present Mic continues using his loud voice against Kyoka and Koji who are unable to handle it. Out of options, Kyoka asks Koji if he can control insects to which he approves. Kyoka uses her Earphone Jacks to break a rock, which reveals dozens of insects, much to Koji's terror. Kyoka tells Koji that she understands his phobia but using the insects to attack Present Mic is the only plan she can think of because their opponent is too strong. Kyoka encourages Koji to follow through with her plan. After seeing Kyoka's bleeding ears, Koji is ashamed that he is running away from this fight and realizes that he can only continue being at U.A. by overcoming his fear. Koji musters up the courage and commands the insects to attack Present Mic. At the escape gate, Present Mic sees that time is nearly up. Suddenly, dozens of insects crawl on Present Mic, who realizes that the insects traveled to him by moving underground; a place where sound is ineffective. Present Mic is paralyzed by fear, allowing Koji to run through the escape gate while carrying an injured Kyoka with him; thus, they pass the practical test.
Back in class at U.A., Koji learns that he passed the written test and will go with his classmates to the forest lodge which is a boot camp. Koji along with his class go to Kiyashi Ward Shopping Mall to buy necessities for the forest lodge.
The next day after the shopping trip, at U.A., Shota informs Class 1-A that the destination for their lodge trip has been changed and the new destination will only be announced on the day of the event. The first semester has come to a close and summer break has begun. On the day of the event, Class 1-A boards a bus that will take them to the forest lodge destination. An hour later, Class 1-A’s bus stops for a restroom break. However, Class 1-A notes that Class 1-B isn’t at the rest stop. Suddenly, two females wearing cat-like costumes and a small boy appear; the females excitedly introduce themselves as the professional Hero Team, The Pussycats. The black haired female explains to Class 1-A that they will be staying at the base of a mountain which is a part of their domain; they have three hours to reach the base of the mountain using their Quirks as they please and those who don’t arrive there by 12:30 pm won’t be served lunch. Soon, Class 1-A realize that they have already arrived at their destination and their training camp has already begun with the Pussycats being their supervisors. Some of Class 1-A try to leave, but Pixiebob uses her Quirk to create a landslide of dirt that causes Class 1-A to fall into a forest called Forest of Magic Beasts, which they must traverse to reach their destination. Suddenly, Class 1-A are confronted by a beast; Koji tries using his Quirk to control the beast but it does not work due to the beast being made out of dirt. Izuku, Shoto, Tenya and Katsuki mobilize and use their Quirks to destroy the dirt beast.
After Izuku, Tenya, Shoto and Katsuki destroy the dirt beast, Class 1-A begins traversing the Forest of Magic Beasts. However, the journey through the forest to the Cabin takes around about 8 hours. Class 1-A arrive at the facility, battered and tired. It is now 5:20 pm in the evening. Pixiebob admits that she thought they would take longer to get to the facility; she praises Class 1-A for figuring out her Earth Beasts quickly and easily. Class 1-A fetch their luggage from the bus and put it in their rooms. Class 1-A go to the dining hall to have dinner. After finishing eating dinner, Class 1-A go to the hot springs. The next day at 5:30 AM, Class 1-A are outside the training camp cabin. Shota greets his students and tells them that they will undergo reinforcement training to strengthen and upgrade their Quirks which will also allow Class 1-A to obtain their temporary licenses.
Quirk and Abilities
Animal Voice (生き物ボイス?): Koji's Quirk gives him the ability to command and control animals. Whatever command he gives, the animal will carry it out. His ability to command and control animals extends to insects as well. However, he is unable to control the animals or insects if they cannot hear his command. Also, he is unable to control artificial animals.
- Koji is student no.9 in Class 1-A.
- He ranked 11th in the Quirk Apprehension Test.
- His name contains the kanji for mouth (口?), field (田?), shell (甲?), and boss (司?).
- He likes nature.
- He is from the Tohoku region of Japan.
- Kohei Horikoshi likes his design as it deviates away from human form.
- Koji ranks 11th in Class 1-A's Grades.
- Koji's first line of dialogue happened in Chapter 66, 61 chapters after his debut.
- (To himself) "That's right. I got into U.A. High, my dream school... At U.A., it's always about moving forward! That's what we tell ourselves... Plus Ultra!!"