NAGA
The engine most players actually meet. NAGA is Dwango’s riichi AI, and it is sold as a review service: paste a Tenhou log and it marks every discard, call and riichi.
Service ↗- Rules
- Four-player Japanese riichi, Tenhou rules 1
- Approach
- Convolutional neural networks 2
- Strength
- Tenhou 10 dan 1
- Access
- Paid review service, from ¥550 a month 1
Who built it
NAGA was developed by Dwango Media Village (DMV), which first described it in January 2019 2. The review service is run by DWANGO Co., Ltd. 1.
Rules
NAGA plays four-player riichi. Its review service accepts Tenhou ranked, tournament and private-room games played with open tanyao, and custom logs analysed under Tenhou’s four-player ranked rules, in East-South or East-only format 1.
How it works
Dwango’s 2019 write-up describes four convolutional neural network models: one for discards, one for calls, one for riichi and one for kan 2. The discard model reads the player’s hand, all four players’ discards and calls, the scores and the count of unseen tiles. The models were trained on game records from Tenhou’s highest-level table 2. To show why NAGA chose a move, Dwango used Guided Backpropagation to highlight which inputs mattered 2. The Suphx paper notes that NAGA did not use reinforcement learning at that time 3.
The current service offers several play styles, including Omega (call-heavy), Gamma (defensive), Nishiki (balanced), Hibakari (very closed-hand), Kagashi (very call-heavy), Ananta (avoids last place) and Ouroboros (plays for first), plus a self-improving type 1.
Strength
NAGA began playing on Tenhou on 22 October 2018 and reached the expert table a week later at 4 dan; by January 2019 its best rank was 8 dan 2. The Suphx paper later recorded NAGA at 8 dan with a stable rank of 6.64 over 9,649 games 3. The NAGA service now states that it has reached 10 dan on Tenhou 1.
How to access it
Sign in to naga.dmv.nico with a Niconico or Google account and join a membership plan, through a Niconico channel or Stripe 1. Plans include points that are spent per analysis. Prices on 24 October 2026 1:
| Plan | Price | Roughly |
|---|---|---|
| Gold | ¥550 / month | 10 East-South games analysed |
| Platinum | ¥1,100 / month | 30 games |
| Diamond | ¥2,200 / month | 100 games |
Besides log review, members can call NAGA into a Tenhou private room or user-run tournament to play against it, and use a quiz built from their own mistakes 1.
Sources
- NAGA service site (naga.dmv.nico), Japanese
- Dwango Media Village, “Mahjong AI NAGA” (21 January 2019)
- Li et al., “Suphx: Mastering Mahjong with Deep Reinforcement Learning”, arXiv:2003.13590 (2020)
Facts checked against these sources on 24 October 2026.