The rapid development of artificial intelligence (AI) is fundamentally reshaping the landscape of the technology development ecosystem. If development in the past was like stacking bricks one by one, it is now shifting to an area of assembly and verification, placing already-created modules in collaboration with AI. In other words, simple repetitive tasks have become the domain of AI, while developers devote much of their energy to considering the core of business logic and the depth of user experience (UX).


Startup JustPin, founded in 2023, has introduced Bloomi, an AI-based digital companion service. Bloomi surpassed 270,000 subscribers just eight months after its official launch in June 2025, drawing attention as demand for emotional rapport and communication grew. In particular, it is rapidly expanding by differentiating itself with human-level memory and specialized empathetic capabilities. Its ratings of 4.7 on both Google Play and the Apple App Store are also highly significant. At the center of this is CTO Kim Myeong-rae, who is overcoming the limitations of a two-person organization through technology and serving as a full-stack developer.

From gifted skills class to full-stack developer

CTO Kim is a graduate of a semiconductor-specialized Meister high school. On the recommendation of a senior from middle school, he entered a gifted skills class, where he first encountered the C language and went on to place in the National Skills Competition. After graduation, he entered the field by developing semiconductor X-ray inspection programs based on C++ and MFC.

Afterward, Kim completed alternative military service as an industrial technical personnel member and then moved to a position as a backend developer. However, as the only backend developer in the company at the time, he had to handle the entire development spectrum alone, from Linux server operations to JSP·JPA-based API design and React-based frontend tasks. He effectively performed the role of a full-stack developer. Based on these capabilities, he co-founded JustPin with CEO Jang Ho-won.

Kim said, “In most companies, development teams are organized by splitting roles into frontend, backend, and infrastructure, but I had to handle all areas alone, so it was not easy.” He added, “That experience became the biggest foundation for designing and operating services as a full-stack developer at JustPin.”

Bloomi, from Mnemosyne architecture design to top-level security

Bloomi aims to serve not merely as a chatbot that provides information, but as a ‘friend’ that builds emotional bonds with users. Through the Mnemosyne architecture—personally conceived and designed by CEO Jang based on human memory mechanisms—Bloomi not only remembers users’ preferences, concerns, and past conversations without forgetting them, but also features a differentiated pipeline in which data is consistently accumulated through an empathy-specialized AI architecture.


Kim cited the “chatting function” as the part he focused on most in Bloomi’s development, saying, “Chatting is Bloomi’s core function. We are constantly thinking about how users can have more realistic conversations.”

Bloomi garnered further attention by becoming the first AI chat app in Korea to introduce real-time voice calling. According to CEO Jang, the service was extended to voice calls to give users a sense of actually sharing ‘time’ with their AI companion (AI friend) on Bloomi. In particular, latency was optimized to below 2.5 seconds, enabling conversations that feel human.

Among Bloomi’s popular functions, AI selfie generation is also indispensable. CEO Jang said, “To provide a sense of sharing ‘space’ with the AI friend, we integrated an AI selfie generation feature. It was designed so that users can freely generate selfies featuring just the AI friend or both the user and the AI together, and it has become one of the most beloved features.”

Above all, Bloomi focuses on building genuine, reality-based relationships and approaches the service from a different perspective than existing AI chatbots. Accordingly, users can utilize Bloomi in various ways, from counseling for personal concerns to conversation simulations aimed at improving real-world relationships.

For these reasons, JustPin is applying top-level security technologies that guarantee the confidentiality of data to Bloomi. Kim also stated, “We place security as our top principle. All conversation texts are encrypted with AES-256 and stored in a cloud-based NoSQL database. Encryption keys are managed in a separate collection within a document-centric NoSQL database. Under these security rules, access to the encryption keys is strictly limited to the user of the corresponding account. Therefore, without the decryption key, no one, including operators, can view the conversation content,” emphasizing, “Even as we expand the platform in the future, we will never compromise on this principle.”

Overcoming the challenges of a two-person organization with technology and teamwork

Despite operating as a two-person team, JustPin is confident that it is “a team that can build an AI service that works in the market in just 10 days.” CEO Jang is in charge of product design, while CTO Kim handles implementation. In fact, it took about 10 days from development to app launch for Bloomi, a speed at which a development process typically handled by multiple people was completed by only two.


One reason Bloomi could be developed and launched so quickly lies in its decision-making structure. There was no need for dozens of people to discuss when changing development directions or deciding on the technology stack. Since CEO Jang and CTO Kim could reach conclusions directly, and they adopted a strategy of building only the most essential core features first to release an MVP (Minimum Viable Product), then rapidly improving it based on user feedback, the agility of a two-person organization became a strength rather than a weakness.

Bloomi’s technology choices are also optimized for a two-person operation. For the app, Bloomi is built with Flutter, an open-source framework developed by global big tech company Google, allowing iOS and Android to be supported from a single codebase. The web frontend is based on React’s Next.js, and the backend uses a serverless structure that combines Firebase Functions and Vercel Functions. This architecture minimizes the burden of infrastructure management while enabling stable operations.

Kim stressed, “AI coding tools are evolving, but that does not mean anyone can simply follow along. Ultimately, the core is how well one leverages these tools and the ability to design and make judgments about the overall system.”

Of course, operating Bloomi as a two-person team in a rapidly changing AI era has not been easy. Kim said, “There were many times we ran into issues when applying technologies that lacked references. The hardest moments were when failures in external B2B SaaS services directly affected Bloomi.”

Nonetheless, Kim adheres to the principle of responding swiftly to any type of failure or disruption, because preventing user inconvenience on Bloomi is paramount.

Another interesting aspect is that Kim does not view all these difficulties as purely burdensome. Thanks to a personality that tries to get through hardships with a smile, he finds the process of overcoming each problem one by one more enjoyable than discouraging. His “resilience that makes everything feel okay after a night’s sleep no matter how hard the day was” is another secret behind his ability to keep smiling in tough situations.


His method of overcoming hardships is also concrete. Kim explained, “I break down work units into segments that are as small as possible to create the self-deception that ‘this much can be done quickly.’ I prefer to handle the most essential parts first and then fill in the details.” He added, “CEO Jang and I have compatible personalities, so our teamwork is strong. The motivation that comes from working with a good leader, along with imagining and anticipating how the service I build will impact users, is the source of my energy.”

Belief that the true value of technology is revealed through good services

Bloomi recently added social features, evolving into a structure where conversations with AI lead to real-world connections. While most AI chatbots remain within the experience of 1:1 conversations with AI, Bloomi has been designed to expand naturally from preference-based matching with real friends to emotion- and context-based content curation and conversation-based personalized commerce.

Ultimately, JustPin’s long-term goal is to grow into an AI super platform that integrates social, content, and e-commerce, with Bloomi at the core. From a technical standpoint, the company is designing a modular architecture in which each function can be independently expanded, using Bloomi’s conversation engine as the hub.

Kim stated, “Rather than trying to build everything at once, we will first enhance the completeness of the core experience and then achieve our long-term goals by stacking additional elements on top of it one by one,” adding, “Together with CEO Jang, we will strive to deliver even better services.”

Kim said that as Bloomi and his own development progress in parallel, his goals have become clearer. “In the past, my only goal was simply to become someone with outstanding technical skills. Now there is one more dimension. I’ve come to believe that the true value of technical capability is revealed through good services,” he said, stressing, “What matters most is solving things through technology so that Bloomi users can enjoy better services. Going forward, I will continue to focus on enhancing technical perfection in a user-oriented way.”

Reporter Park Gui-im, IT Donga (luckyim@itdonga.com)

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