First-ever Lightning Network hackathon in Japan: “Offchain Academy Hackday”: Report

7 min readOct 10, 2018


Hosted by Imai-san of Offchain Academy and co-hosted and supported by HashHub, the first full-scale Lightning Network hackathon in Japan was held on September 29 and 30, 2018.

Companies and groups that conduct research and development on Lightning Network (LN) are on the rise in Japan as well. However, there aren’t that many developers who understand LN technology yet, therefore this time we aimed to host an event which serves as an entry to LN development for those who are “interested in LN and have experiences developing using web services and APIs”

The judges included companies such as Nayuta, IndieSquare,chaintope that are at the forefront of Bitcoin and LN development in Japan, who helped our event by providing technical advice to participants and APIs as well as reviewing of presentations.

A total of 30 developers in all gathered in this event. They learned the basics of LN for two days to the point of implementing Lapps each team came up with. We certainly had a very high-energy and high quality event.

Overview of Event

During the first half of Day 1, teams received a lecture on the basics of how Lightning Network works and developer tools.

BTCPayserver basics

Nicolas Dorier, the lead developer of BTCPayserver(BTCPS) as well as HashHub adviser had lectured on the overview of BTCPS and development of LN nodes.

By utilizing BTCPS, one can easily set up Lightning full-node (c-lightning and lnd). At the hackathon, almost all teams used BTCPS for their development.

Lightning Network Basics

Kurimoto-san, CEO of Nayuta, the developer of original Lightning implementation, “Ptarmigan” had lectured us on the basic structure of LN. Structures on Lightning and how Bitcoin onchain transaction works, and what he considers to be the complexities of LN were covered. Also how to set up Ptarmigan which is currently being developed was explained.

Presentation document is here

Unity SDK for Lightning Network

At IndieSqure, an SDK which can embed Lightning payment in games using Unity are under development. Christian Moss, the CTO introduced actual examples; games which embedded the SDK.

There are already many Lapp games which utilized two-way micropayment on LN, and more Lightening games built with Unity are likely forthcoming.

Presentation document is here.

Introduction of Lapps

We had a lecture from Imai-san, our host, on examples of actual applications of Lapps using current LN. Current representative Lapps such as application to hardware, second-by-second micro-streaming charging, API-by-API charging, and application to games were covered.

Presentation document is here.

Ideathon & Implementation

After basic explanations on LN are covered, teams consisting of a few people were formed, and each team started to brainstorm ideas. At this point, there were still people who didn’t quite understand the mechanics of invoice on LN and how to design a payment channel, but with advice from hosts and judges, ideas started to materialize.

Second half of Day 1 — First half of Day 2: Implementation

Nothing but diligent implementing. The judges of Hackathon placed emphasis on originality of ideas as well as whether works have progressed to the point of actually functioning, therefore teams kept on pushing until the very end.


After two day of workshops, planning and implementation, 7 teams in all presented their achievements in front of us.

The Judges: Kurimoto of Nayuta, Azuchi of chaintope and Moss of IndieSquare from the left

Team Shinagawa

1. Auction system using LN

2. The actual scheme is bidding on auctions with transaction on LN. If there were bids above one’s amount, the previous bid will be returned. Transaction fees on LN are cheap, so additional transactions do not cause issues.

3. Because the bid amount must be committed on LN in advance, it is impossible to bid above one’s ability to pay, therefore there won’t be refusal to pay after the successful bid.

4. Future challenges are: it is not trust-less with regard to refund from auction operator without use of smart contracts.

Presentation document is here (English after Japanese)

Team Vote

1. Voting system using LN

2. The scheme of real-time voting result tracking using real-time-ness of Lightning

3. In this implementation, payment of 10 satoshi = 1 vote, issuance of invoice (voting request) with LN payment, and real-time view of voting result implemented.

Presentation document is here

Team Green Freedom

1. Micro-charging service of digital Manga using LN

2. Micro-charging with LN with each scroll of screen. Pay-as-you-read scheme.

3. Also by pressing “Like” on each work’s page, one can donate to the Manga artist as well as use payment as vote. Social-function is added to the micropayment.

4.Actual implementation is complete, and Lightning charge from will be available

Presentation document is here

Team Murasaki

1. Devised and implemented a camera which can be used by Lightening charging

2. By installing LN-enabled camera in event venues and theme parks, users can be charged for each photo

3. By utilizing real-time-ness of LN, the photo will be taken the moment payment is received

4. By using such a scheme, it may be possible to devise hardware-on-loan which is based on (monthly) subscription model.

Presentation document is here

Team Kayac

1.Micro-charge service of on-line calls of one-to-many using Lightning

2.By combining with, second-by-second charging is done. When session is disconnected, charging stops.

3.It is also possible to use it for not only one-to-one but one-to-many session as well. For example, during live-streaming of Youtubers and game-live-streamers, multiple viewers can be charged for the streaming easily.

4. As for implementing, by using WebSocket, exchange of invoice between distributor and users can be automated

Presentation document is here

Team Cherrychain

  1. Combination of hardware and LN. Pay-as-you-use hardware.
  2. Implemented hair dryer which can be charged each 10 second with LN. Demo successful.
  3. Using RasberryPi, the plug was hacked, improved so that on/off switch responds to LN payments.

Presentation document is here

Team BlueBird

  1. Influencer ad using LN
  2. The current influencer ad model has the problem long cycle from appearance of ad to payment, and advertisers have hard time planning in details click-by-click.
  3. By using LN, it seems possible to have detailed and fast, click-by-click receiving and payment of ad revenue.
  4. By using implementation of Lit, utilized push-type issuing of invoice

Presentation document is here

The result of review

HashHub award

We initially were planning to have just a single award, but due to a number of high-level presentations, we came up with HashHub award for two teams on the fly. (These teams were awarded with 1 month use of HashHub space)

Team Cherrychain(LN-enabled Plug and Dryer demo)

Team Kayac (one-to-many online streaming charging with LN)

Grand Prize

…and now, the prestigious grand prize of 1st-ever Lightning hackathon goes to…

Team Green Freedom

Not only embedding micropayment with Lightning to digital comics, but they were thoughtful in details such as social functions and error-handling. Also, they successfully implemented functions which are ready to go live, which was seen favorably by the judges.

General Comment

Since this was the very first Lightning hackathon held in Japan, we didn’t know exactly what level of products we could expect, but the teams surely exceeded our expectations with their products and ideas. We would say it was quite a meaningful event. The member who participated in Berlin Lightning hackathon also commented that this hackathon was on par with overseas hackathons in terms of quality. We believe we are seeing formation of strong developer community in Japan.

Still, what the teams could create in just two days were rather limited, and by continuously hosting hackathons and study meetings, we would like to incubate even higher-level related technologies, products and ideas from Japan to the world.

At HashHub, we plan to not only actively host and support Lightening Network-related events, but set to releasing our own product which will accelerate the use and development of Lightning network, out in October.

Also we would like to actively collaborate with overseas event and hackathons, so if you are event hosts and interested in collaborating, please get in touch with us (email: ).




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