Debuting in Arc 3, Otto and Subaru initially started off on a rather hostile note, after their first incident with the Hakugei. After their paths crossed for the final time in that same Arc, Otto accompanied Subaru and Emilia to the Sanctuary and acted as one of Subaru's biggest supporters, proving crucial to Subaru's plans and allowing him to defeat Roswaal and overcome the Sanctuary incident. In the following year, Otto joined Emilia Camp, acting as their Head of Internal Affairs. He also played a crucial role in Arc 5, helping in warding-off two of the three Sin Archbishops of Gluttony, at a cost of suffering a serious injury to his legs.
Otto has gray hair that is quite long. He has sharp, bright blue eyes and a fair skin tone. He is considered to be somewhat handsome if he has a serious expression, however, he is usually either retorting, shouting, or panicking, ruining his looks. He has a medium build, but has trained himself since he used to work as a merchant. He wears a green, belted wardrobe, as well as a dark green hood, held up by a red bow. He also wears a green Ushanka with a white feather.
Otto is quite an unlucky person, first shown when he almost drowned in his first bath; he was accordingly born under an unlucky star. When he was young, he was treated as a pitiful child by others due to his Divine Protection, as they thought he was talking to imaginary objects. He is generally on the receiving end of jokes, with some people such as Natsuki Subaru suggesting to use him as a shield, but despite this, he is loved by the others. He's easily embarrassed, sensitive, and considered weak or pathetic, which can lead to others underestimating him. He is also sometimes cowardly and prone to panic; after learning the Hakugei was after Subaru, he pushed him out of his cart--though ultimately he still died in this timeline. However, he isn't totally bereft of virtue. He is very loyal to his friends; he helped Subaru in the Sanctuary even though it could've cost him his life, that not being the first time he's risked himself for his friends.
20 years before the beginning of the story, Otto was born in Picoutatte. To his "luck", he was blessed with a Divine Protection of Soul Language which allowed him to hear voices and communicate with non human beings. Ever since birth, Otto's life was living hell. He would non stop hear different sounds and voices, screams and death cries; it was so bad that even when his parents picked him up and talked into his ear, Otto was unable to hear them, let alone understand the meaning of their words and actions. As a result, Otto grew up without any emotions. He did not cry, he did not get angry, he did not get happy; all because to him, everything sounded like the exact same thing. His parents strived to understand what was wrong with their son but to no avail. At the end, their love for young Otto slowly faded and they started to pay more attention to his siblings. When Otto was five years old, his older brother presented him with a notebook and a pen, began teaching him how to write and communicate without speaking. Due to Otto's inability to hear, it took him ten times longer to learn how to write than it took an average kid, but that did not demoralize him as he saw it as a way to kill some time. One day, he presented a piece of paper in front of his parents saying "thank you for everything" which utterly broke them. Coincidentally, it was also the first time Otto cried since he was born, as he finally realized the love his family harbored towards him and it opened up his heart.
When Otto turned 8, he was able to differentiate the human and animal world much much better than before. Sadly, his late realization meant his knowledge and education was far behind his age group, but to everyone's amazement, he showed significant talent and will for learning. But sadly, things didn't go as smoothly as everyone hoped; Otto fell behind in a subject called "human relations" and was gradually isolated from his age group, leaving him without any friends.
At the age of 10, Otto finally learned how to truly differentiate between voices, which gradually led him to a realization that he possesses a Blessing. As soon as he confirmed his assumptions, he darted towards his older brother whom he trusted the most and explained everything to him. His brother was rather impressed with Otto's ability but warned him of the dangers that could appear if he ever revealed his ability to others; Divine Protections are god's gift and some people would feel extremely jealous and start hating him for his power. Low and behold, 3 days after the conversation with his brother, the news of Otto's Divine Protection spread around the entire town after his younger brother carelessly told his friends about Otto's blessing. Otto was forced to demonstrate it in order to prove that his younger brother was not lying and from that day onward, he gained a new nickname; Zodda bug bastard.
Throughout the following years, Otto slowly managed to conceal his depressing past and got rid of the vile nickname. But of course, Otto's luck soon ran out as he got entangled up in a love affair with a daughter of a powerful figure in Picoutatte and was accused of a "crime" he did not commit. Otto being Otto, called forth his bug friends who explained the truth to him and Otto carelessly revealed it to the whole town, saying she slept with eight different guys and he was not among them. Out of rage and shame, the girl hired an assassin. Otto lost every ounce of respect and was hated by everyone; he was subsequently exiled from his hometown. His father managed to get a friend of his to take Otto under his mentorship and at the early age of sixteen, he set out into the world as a travelling merchant.
Throughout the following four years, Otto's bad luck really came forth; if he was transporting fruits, bad weather would come forth, if he took a shortcut, random bandits would attack him and so forth. Luckily, Otto was born with a mercantile talent as great as his luck was poor. He rarely lost bets and deals, no matter the odds and of course, he never went bankrupt. One day, Otto misread the market trends and got into a lot of debt after the price of the oil he was transporting plummeted. Luckily, a friend of his told him about a great offer; one where he'd only have to transport someone to a specific place. But once again, Otto's luck ran dry and he was captured by the Witch Cult. Just before he was about to be killed by the Witch Cultist, Ricardo Welkin came to the rescue. After his successful rescue, Otto Suwen met Natsuki Subaru.
Divine Protection (加護 Kago):
Otto has the Divine Protection of Soul Language (言霊の加護 Kotodama no Kago), which allows him to communicate with creatures, allowing him to comprehend their speech. In his formative years, the words of creatures were incomprehensible to Otto, who had no explanation for the constant chattering he heard. However, as time went on, he began to understand more and more of what the animals were trying to say until he eventually fully understood their speech. He also learned to block his power to a certain extent, giving himself reprieves from the constant background noises. Although he was unable to control the actions of creatures, he was able to make them do what he wanted if they themselves wanted to. By communicating with the birds and the insects always hidden from view, Otto possessed a sort of intelligence network that could tell him about circumstances happening far away. However, as he speaks in the language of the creature he's talking with, it makes him look shady to others while he's using it. As Otto can't use it properly, he normally keeps it disabled. Continuous use of this Divine Protection causes him to bleed out from his nose.
Magic User (魔法使い Maho Tsukai): Due to tutoring he received as the son of a merchant, Otto has the capability to use Earth Magic.
- Dona (ドーナ): The user summons one earth wall from the ground. It is typically used for defense, but it can be applied for offense and evasive movement.
- El Dona (エル・ドーナ): The user conjures a swarm of earth mana and pinpoints it at a target, which then bursts into spikes inside them expanding outward. This magic was cut from the Light Novel.
- UI Dona (ウル・ドーナ): Otto is able to lift thick walls of earth around himself in a shape of a dome.
- Al Dona (アル・ドーナ): User summons an enormous blast of violent earth mana that shreds a target and the surrounding area upward. It's strong enough to pulverize the surrounding trees. Otto cannot use Al Dona normally, because he barely has above average magic talent.
Spirit Arts Potential: The Author has stated Otto does have potential to become a Spirit Arts user, as his Divine Protection allows him to speak with lesser spirits, but the spirits ignore him.
- According to the author, Otto's birthday is March 24.
- Otto likes spicy and bitter things.
- He's stated to be very talented in football. If he was born in Japan, he'd most likely make a living out of it.
- In the Emilia Camp, Otto plays a rather interesting role; whenever someone has some trouble regarding something specific, they always ask Otto for advice.
- In Arc 4, Otto for some reason did not appear in Roswaal's Book of Wisdom which completely threw Roswaal's plan off, resulting in Subaru gaining a chance to defeat him and win their bet. He is the only character that hasn't appeared in the Book of Wisdom.
- In the side story The Three Idiots Set Out! Cursed Goddess Statue Episode, he had cross-dressed once under the name "Audrey".
- Otto has his own named chapter in Arc 4, in both the Web and Light Novels, as well in the Anime.
- "The language blessing essentially allowed a person capable of conversing with any living things" Re:Zero Light Novel Volume 9: Chapter 5. Section 4
- "The oozing nosebleed might have been from pushing his brain beyond its capacity" Re:Zero Light Novel Volume 13: Chapter 5. Section 3
- "As a result of employing magic that should have been beyond his reach in this lifetime, Otto was out of breath." Re:Zero Light Novel Volume 13: Chapter 5. Section 3
- "I actually have a talent for football, but it will never blossom because there is no football in that world." Otto Birthday Q&A
- "Coming under Roswaal's attention for the very first time, Otto's face faintly stiffened. His words made Roswaal draw himself up, twisting his neck with a rare expression of simple confusion." Re:Zero Light Novel Volume 14: Chapter 5. Section 2.