Otowa

Credits

Otowa's characters, scenes and art are original. These are the voices and tools they're made with.

Voices

Every voice is synthesized with VOICEVOX, under each voice's own terms.

  • VOICEVOX:冥鳴ひまり: Shizuku · terms of use
  • VOICEVOX:春日部つむぎ: Yuzu, Young woman, Traveller, Kouta's mother, Mei · terms of use
  • VOICEVOX:中部つるぎ: Kiri, Archer, Kanon, Raika · terms of use
  • VOICEVOX:東北イタコ: Tsuru, Mizuki-sensei, Ume · terms of use
  • VOICEVOX:玄野武宏: Hayato, Student, Swordsman, Guard, Daichi · terms of use
  • VOICEVOX:青山龍星: Yamikage · terms of use
  • VOICEVOX:麒ヶ島宗麟: Gantetsu, Old man, Kouta's father, Shopkeeper, Goro · terms of use
  • VOICEVOX:猫使アル: Kouta, Ren · terms of use
  • VOICEVOX:白上虎太郎: Jin · terms of use

Fonts

All under the SIL Open Font License 1.1.

Word frequencies

Ear Power and how often each word is heard come from TUBELEX-JA, word frequencies from the subtitles of about 100,000 Japanese YouTube videos, by Adam Nohejl and colleagues at NAIST (Nohejl et al., 2025), under the BSD 3-Clause License:

The licence
BSD 3-Clause License

Copyright (c) 2022-4, Adam Nohejl
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this
   list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice,
   this list of conditions and the following disclaimer in the documentation
   and/or other materials provided with the distribution.

3. Neither the name of the copyright holder nor the names of its
   contributors may be used to endorse or promote products derived from
   this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

The order in which new words are taught follows the anime frequency list of Jiten, built from the Japanese subtitles of thousands of anime, with words and readings from JMdict (the Electronic Dictionary Research and Development Group). Both are licensed under CC BY-SA 4.0; Otowa's adapted copy of the list, which only its builders use, is shared under the same licence.

Software

Built with open-source software, each under its own licence: Next.js, React, Tailwind CSS, Motion, GSAP, Three.js, React Three Fiber, drei, Lenis, WanaKana, ts-fsrs, Zod.

Otowa's animated guide can use the Live2D Cubism SDK for Web by Live2D Inc., under the Live2D Proprietary Software License and the Live2D Open Software License.

Art

Otowa's illustrations were made for it, from its own character designs.