Hello. I'm Jeonghoon Kim from the Redis team at LINE Plus. From July 2nd to 4th, I participated in the internal hackathon "Hack Day 2025". Hack Day 2025 was held at the LY Corporation office located in Kioicho, Tokyo, just like last year (please refer to "Thoughts about Hack Day from Tech Week 2024!" for a review of last year's event).
In fact, I participated in Hack Day last year too. I hope to share the joys of the internal hackathon Hack Day with you based on my two years of experience.
What is Hack Day?
Hack Day is an internal hackathon event that was held annually by Yahoo! JAPAN before the merger. Starting in 2007 and continuing even after becoming LY Corporation (LY) due to the merger, it has reached its 19th year now.
Hack Day is a 24-hour event over two days, ending with an awards ceremony the next day. Notably, during this period, another annual LY event, the tech conference Tech-Verse, is also held. A lively review of Tech-Verse will soon be posted on this blog, so please stay tuned!
Being an internal hackathon, there's no need to find a connection with your job. Because it's conducted under a completely free theme, you can develop the product you want. Additionally, the event isn't just for developers. Designers, planners, HR, and anyone else within the company can leverage their strengths to become Hack Day participants (hereafter referred to as hackers).
Team composition?
Not only can you choose any topic, but teams can also be freely formed. You can gather with people from the same corporation to form a "General Team", or, true to the global nature of the company, you can participate as a "Global Mixed Team" with people from branches in other countries. Last year, I participated as a Global Mixed Team with former members from ex-Yahoo! JAPAN's Redis team. This year, I formed a General Team with people from Korea with whom I recently started collaborating. I thought that forming a hackathon team with people I would work closely with would be a significant advantage for future collaborations, so I did it in this way for two consecutive years.
Even if colleagues around you aren’t interested in hackathons, or you want to participate with international colleagues but don't know anyone, there's no need to worry. The Developer Relations team (DevRel team) organizes meetups for team matching. Many people around me actively used these meetups to participate. Team matching meetups involve members from various countries and regions and are conducted using online collaboration tools like Zoom and Miro, considering the characteristics of the Korean branch adopting the Hybrid Work 2.0 work system.
Planning and verification
Each team had already come up with a rough idea during the process of team formation and pre-judging. From the announcement of the participants, they began to concretize plans, conduct technical reviews, prepare environments, and so forth. It's a platform where everyone can pursue their dreams with a free theme, leading to doing things unrelated to their primary job quite often (yes, that's the story of my team). Preparations were conducted to the level of simply validating ideas without compromising the event's original intent of "creating within 24 hours", leaving serious development for Hack Day.
Our team frequently works remotely due to the company's adoption of Hybrid Work 2.0. To make quick decisions during the planning and verification process, we held two or three offline meetings. Furthermore, in our company, employees are given a "Travel Day" during business trips, allowing time to focus on work during transportation or at the business trip location. We used this time to gather for one final review.
Once the technical review was done and plans were solidified, we could really feel Hack Day was starting (although plans changed frequently during development 😂).
Sharing the authentic Hack Day experience!
The long-awaited first day of Hack Day, I visited the office with excitement and received the visitor's badge for the business trip period at the reception. I was also serving as a "LINE DEV Reporter" to cover and document Hack Day, so I arrived at the office somewhat early to faithfully fulfill my duties. Some teams had already started meetings.
Due to the large number of people, the event space occupied an entire office floor, and team spaces were separated. Thinking back, I felt comfortable throughout Hack Day, perhaps because a larger space was rented compared to last year, reducing the population density and providing an environment conducive to development.
Hack time!
Being an annual event, there's a tradition where all hackers gather to declare the opening. At 9:00 AM on the first day, everyone gathered to collectively shout "Hack Day!", signaling the official start of the hackathon.
Immediately after the opening ceremony, all hackers sat down without delay and began development. The total of 24 hours is a time frame that can be considered both long and short, and even minute differences can affect the level of completion. Therefore, everyone started racing towards "Perfect the Details". It was impressive to see everyone utilizing all available resources, such as monitors prepared in the venue and whiteboards placed throughout.
Never-ending development, and never-ending snacks
Even before joining the company, I've attended hackathon events here and there. Although it's embarrassing to admit, I consider "endless snacks" to be the highlight of a hackathon. It may seem trivial, but consuming sugar and caffeine is truly crucial when mentally exerting yourself rapidly in a short period. Whether they read my mind or the organizers of hackathons universally feel the same, snacks were continuously provided throughout the two days of Hack Day. There were rest areas set up throughout the venue where snacks were always available.
Not only were the same snacks constantly replenished, but donuts were prepared for the afternoon when sugar levels tend to drop, and cup noodles were available for the hungry nighttime. The DevRel team's sense of menu selection was commendable. Moreover, hackers from each corporation around the world brought snacks from their home countries to the rest areas, enhancing the feeling of camaraderie.
The chaotic development experience
During this Hack Day, we wanted to create something to make work environments more enjoyable, all while having fun. Based on this thought, we drew inspiration from the concept of the "Scouter" in the Dragon Ball series and thought it would be entertaining to create a program that measures each individual's "power level" based on communication records. In online work environments, communication is most actively conducted through Slack, our work messenger, so we planned a program that appropriately utilizes the Slack bot and AI model to calculate power level.
Of course, the specifics of this plan changed constantly throughout development. Initially, we wanted to express power level in terms of "attack power" and "defense power", but realized this program, meant to be light-hearted, could unintentionally hurt someone. So instead of such direct and ambiguous expressions, we changed it to a more professional and intuitive format. We incorporated the well-known psychological model "Big Five personality traits", using the five traits from Big 5 Personality to display them in a form reflecting character attributes in games.
We initially planned to physically print this result. By using AI to reinterpret profile images and offering printed cards with the results, we thought it would allow participants to cherish this Hack Day memory for a long time, making and providing unique cards with a photo printer to everyone who visited the venue.
After modifying the prompts several times, the Big 5 Personality results and AI images were complete, and it was time for printing...but even after changing the film several times, the photo printer didn't work properly. Faced with a hardware issue at the last moment, we eventually had to change the plan to provide download functionality in file form. 😂
Here's the final result completed after many trials and tribulations!
Presentations, judging, and awards to conclude Hack Day
The third morning dawned. Hack Day is not merely about development over two days. The third day marks the grand finale of Hack Day and is arguably the most crucial day.
Presentation: Appeal in 90 seconds
The first schedule for the third day is a presentation session where each hacker showcases their products. Here, Hack Day's unique characteristic caught my eye; each presentation is restricted to precisely 90 seconds. Ninety seconds is not enough time to introduce the technology fully and demonstrate a live demo, but the efforts by hackers to make an impact within that short time is part of what makes Hack Day enjoyable.
These "90 seconds" are strictly measured, and once you reach the time limit, it doesn't matter who you are, your microphone is turned off. There were teams that had their microphones turned off while speaking due to insufficient time, but such moments acted as moments of levity, inducing laughter and leaving a lasting impression. The seemingly short yet sufficient "90 seconds" rule prevented the session with presentations from dozens of teams from becoming monotonous, keeping listeners engaged.
Booth operating: Judging and full-fledged networking begins
The second sequence is booth operating time. As 90 seconds isn't enough to display everything or allow direct experiences, this session was arranged. Immediately after the presentations, booth operation time began.
Judges, who might find it difficult to judge all the dedication and effort with only 90 seconds, used this time to visit each booth and thoroughly review the results. Judging was broadcasted live online to involve members from various countries worldwide.
The hackers also enjoyed the event from their spots. Even without any guidelines, all hackers from participating teams took turns guarding their booths and visiting others. In fact, the last two days were dedicated to development, leaving no time to look around. Now we had the chance to network, greeting the adjacent teams and sharing each other's ideas.
The products created by hackers shine only when they garner users' interest. Therefore, this time was precious for everyone to receive rewards for their two days of effort.
Awards ceremony: Time to receive some real rewards for our efforts
While interest and pride are certainly valuable, aren't tangible rewards even better? Although people didn't outwardly show it, I think everyone was eagerly anticipating this moment the most. The limited number of awards making them even more valuable.
Let's take a look at the dopamine-filled moments captured during the award announcements.
Listening to the award speeches, it seemed like many new employees who hadn't yet been assigned to teams in Japan participated. Demonstrating that the ability to create excellent products isn't bound by seniority or job role, many teams composed solely of new hires won awards. This made me feel that LY's future is indeed bright. 😆
Work hard, play hard
The award ceremony is over, so what more is left, you ask? Now it's time for the after-party! During the awards ceremony, I wondered why the DevRel team members were absent, and it turns out they were preparing a grand feast for the hackers.
Starting with a Japanese traditional play, the gathering for camaraderie began. It was time to vent about the last three days while enjoying food and a bit of drink. Despite the differences in branches, nationalities, and languages, the hackers put their hearts and minds together to thoroughly enjoy the end of Hack Day. Though parting was tinged with regret, everyone stuck around until late, making the most of the final moments together. Once again, everyone put in a great deal of effort!
Reflecting on Hack Day
Although it was a hectic week, looking back, it was a valuable time where new technologies were encountered, conversations with colleagues from other corporations were shared, and camaraderie among team members was strengthened. I believe Hack Day not only offers numerous enjoyable elements but also injects immense motivation into handling core tasks. These aspects, I think, are what drew me to participate in Hack Day two years in a row. I'd like to take this opportunity to express my gratitude to the DevRel teams from various countries that plan and lead this event annually.
Now, I'm back to my main work, looking forward to next year's Hack Day with renewed energy. 🙂 Hackers, let's meet again at the next Hack Day!
