Doki Doki Integrates Chainlink VRF for Provably Fair Randomness in NFT Gachapon Machines

5 min readAug 28, 2021

We are excited to announce that the all new Doki Doki NFT Gachapon machines are powered by Chainlink VRF, the industry standard for smart contracts needing a tamper-proof and publicly auditable random number generator (RNG). Our first Chainlink VRF enabled Gachapon — Zodiac Girls — launches today and continues the Doki Doki tradition of creating the most fun and fair way for collectors to obtain amazing NFTs and for artists to launch their own collectible series.

We’re always looking for ways to improve the experience of our users while also making sure we use the latest technology to enhance security. Our integration with Chainlink VRF makes Doki Doki Gachapon machines more secure, fair, and reliable than ever before while providing an improved user experience. (◕ᴗ◕✿)

Doki Doki enables artists, brands, and projects to deploy and manage custom digital Gachapon machines that use randomness to gamify the distribution of their NFTs. Players of Gachapon receive capsules containing randomized NFTs, similar to opening a pack of cards. Chainlink VRF is an innovative solution to the challenges of generating secure and unbiased randomness for smart contract use.

“Using Chainlink VRF is the best way to help ensure our system is fair and can’t be gamed, as users can independently verify the RNG solution worked as intended.” — Kirienzo, Doki Doki CTO

Let’s dive into some specific benefits of the integration and how it works.

More Reliable Results

In rare instances, block-reorgs can cause players to receive a different NFT from the one they saw upon opening a Gacha ball, leading to a frustrating user experience. Chainlink VRF solves this problem through a tamper-proof randomness solution (described more below).

Play History and UI/UX Changes

Play History has arrived! A log of your Gachapon plays can now be accessed from the collection page. Here you will be able to claim any previously unclaimed NFTs, and audit the RNG results from Chainlink VRF.

For new machines that use Chainlink VRF, you will need to complete an additional “claim prize” transaction to retrieve the NFTs into your wallet. There’s no time-limit, you can always claim your prize later in your Play History.

Note: Play history is unavailable for previously launched Gacha machines which do not use Chainlink VRF.

MEV Attack Protection

RNG methods that rely on block variables are known to be vulnerable to Miner Extracted Value (MEV) attacks. MEV attacks are essentially ways to game the way blocks are written to the chain and allow miners to make money from trades at the expense of normal users. The higher the value of the NFTs, the higher the likelihood of MEV attack, as there is an economic threshold for when MEV attacks become profitable for the miner.

At a high level, Chainlink VRF protects our Gachapon machines from MEV attacks by using oracles to provide our smart contracts with pre-verified random numbers. Each time a Gachapon is played, a request is sent to Chainlink VRF which returns a set of random numbers consumed by the machine smart contract to fairly determine the NFTs won by the player. Now, both players and machine owners can feel at ease knowing that the RNG method used is provably-fair and wasn’t manipulated or predicted by the users, oracles, or Doki Doki team.

For a detailed explanation of how VRF works, check out the official blog post by Chainlink.

Zodiac Girls! The first Chainlink VRF-powered Gachapon Machine!

The first Gachapon machine to use Chainlink VRF will be Zodiac Girls — an exclusive set of 24 collectible, anime-themed NFTs inspired by the twelve Zodiac signs. Secret rare editions are animated and limited to 1 of 1, while rares editions have 10 copies each. All NFTs are minted natively on Ethereum and bridged to Polygon so players can enjoy near-zero gas fees. Good luck to all players and may you find your personal zodiac girl! Play here | Tutorial

Zodiac Girls! Artist: Orendi Laran | Play here | Tutorial

About Chainlink

Chainlink is the industry standard oracle network for powering hybrid smart contracts. Chainlink Decentralized Oracle Networks provide developers with the largest collection of high-quality data sources and secure off-chain computations to expand the capabilities of smart contracts on any blockchain. Managed by a global, decentralized community, Chainlink currently secures billions of dollars in value for smart contracts across decentralized finance (DeFi), insurance, gaming, and other major industries.

Chainlink is trusted by hundreds of organizations, from global enterprises to projects at the forefront of the blockchain economy, to deliver definitive truth via secure, reliable oracle networks. To learn more about Chainlink, visit chain.link and subscribe to the Chainlink newsletter. To understand the full vision of the Chainlink Network, read the Chainlink 2.0 whitepaper. Want to discuss an integration? Talk to an expert.

About Doki Doki

Doki Doki is a NFT marketplace featuring Gachapon machines that make buying and selling NFTs easier, more fun, and more fair for everyone. Gachapon (ガチャポン) refers to Japanese vending machines that dispense capsules containing a mystery collectible, similar to blind boxes. Doki Doki enables artists, brands, and projects to launch their very own digital Gachapon machines and load NFTs inside for others to play and obtain.

$DOKI and $AZUKI are the two tokens which power the Doki Doki ecosystem. Their use-cases include Buybacks, Staking, Yield-farming, NFT Farming, and more to come in the future.