Messages, mentions, menus, and group context.
SIDE PROJECTS · 01 / LIVE PRODUCT
What if translation stayed inside the conversation?
Nihongo Buddy is an AI-powered LINE bot for multilingual group chats. It translates naturally, explains meaning on demand, remembers context only when invited, and handles its own usage and credit controls.
AI PRODUCTFULL-STACKCLOUD-NATIVEMONETIZED
‹
日
Nihongo BuddyGroup translation · 3 members
•••Tomorrow at 7 works for me!
明日の7時で大丈夫です！
EN → JA · casual駅で会おう
Let’s meet at the station.
JA → EN · natural＋
Message
➤Natural translation stays in the group chat.
THE FRICTION
Copy. Switch apps. Translate. Paste. Lose the moment.
THE PRODUCT DECISION
Put the intelligence where the conversation already happens.
02 / SYSTEM ARCHITECTUREA complete product,
A complete product,
not an API demo.
The visible experience is a simple bot. Behind it is a production system that routes events, applies group settings, protects privacy, meters usage, processes payments, and returns the right response to LINE.
Webhook routing, modes, validation, and response control.
Translation, explanation, and context-aware replies.
Credits, settings, usage, and opt-in encrypted memory.
LINE Messaging API
Webhook events and replies keep the entire experience inside LINE.
OpenAI API
Natural translation and mention-driven conversational support.
Python · Flask
Application logic, usage controls, caching, and service orchestration.
Google Cloud Run
A deployed, scalable service rather than a local prototype.
Firebase · Firestore
Group-level settings, balances, usage, and encrypted opt-in context.
Stripe Checkout
Prepaid chat credits with payment events updating group balances.
03 / PRODUCT & ENGINEERING DECISIONSThe hard part is
The hard part is
designing the rules.
The project required choices across product, architecture, privacy, reliability, and monetization—the same systems thinking I bring to operations.
DESIGN FOR THE REAL UNIT OF USE
Credits and settings belong to the group.
The bot serves a shared conversation, so usage, language preferences, and balances are managed at group level rather than forced into an individual-user model.
PRIVACY BY DEFAULT
Translation works without retaining message history.
Memory is off by default. Groups can opt into an encrypted rolling context, and turning it off clears that stored memory.
CONTROL COST WITHOUT HURTING FLOW
Meter usage quietly; expose the controls clearly.
Free trial credits reduce adoption friction. The in-chat menu shows balances, languages, memory settings, and the path to add credits.
SHIP THE WHOLE LOOP
Payments are part of the system.
Stripe handles checkout and sensitive payment data; signed payment events update credits without turning the bot into a billing application.
WHAT THIS PROJECT DEMONSTRATES
I can move from an ambiguous human problem to a working product—and own everything between the idea and the operating system.
01
Product discovery and user-centered design
02
AI and third-party API integration
03
Cloud architecture and data design
04
Privacy, monetization, and operations
NIHONGOBUDDY.COMLive, public,
Live, public,
and built to be used.
See the product, review its privacy model, or add Nihongo Buddy to LINE.
Open the live project ↗