LiberWerk Advisory

Engineering Leadership,
Redefined.

I help startups and technology companies build world-class engineering organisations — as an advisor, fractional CTO, or VP of Engineering.

Work with Me See Services
9.5M+
Daily Active Users
Japan's first unicorn C2C platform
99.9%+
Service Availability
SLO-driven at hyperscale
~50
Engineers Managed
At peak as CTO, TSE-listed
4–5×
Org Growth Delivered
Engineering org built from scratch
B2B · C2C · B2B2C
Product Models
Cross-domain product leadership
SWE → EM → CTO
Engineer-born Executive
Wrote the code. Built the team. Led the org.
50×+
System Scalability
Hyperscale architecture, SRE-led
EN · JP · KR
Working Languages
Trilingual leadership
What I Offer

Advisory Services

Tailored engagements for companies at every stage of engineering growth.

⚙

CTO-as-a-Service

Fractional CTO engagement for early-stage startups that need executive technical leadership without a full-time hire. Strategy, architecture, and team building.

Monthly retainer 3 months+
◈

VP of Engineering Consulting

Scaling engineering organisations from 5 to 50+. Hiring frameworks, performance management, org design, and cross-functional alignment.

Project-based Flexible
◎

Technical Advisory

Long-term advisory for founders and engineering leaders. Architecture review, technology strategy, and hands-on mentorship.

Monthly retainer Ongoing
▷

Engineering Process & CI/CD

Microservices architecture, DevOps transformation, and CI/CD optimisation. Built on experience from Mercari and CircleCI.

Spot / Project 1–3 months
◎◈

Engineering Talent & Hiring

Full-cycle engineering hiring — from strategy to execution. Job description design, interview process architecture, hands-on technical interviewing, and recruiter network access to source Software Engineers, Engineering Managers, Tech Leads, and VPoEs.

End-to-end Project-based Recruiter Network
Talks & Publications

In Public

Conference 2021

GopherCon

Presented on Go and microservices architecture at Mercari scale.
Conference 2021

gRPC Conf

Spoke on gRPC and Protobuf adoption in production microservices.
Blog 2019–2022

Mercari Engineering Blog

Published technical articles on microservices, Go, and engineering culture.
Open Source 2020

Uber Go Style Guide (KR)

Korean translation of the Uber Go Style Guide — widely referenced in the Korean Go community.
Background

Experience

May 2026 – Present Current
Mantra Inc.
Technical Advisor to CTO May 2026 – Present

Providing strategic technical advisory directly to the CTO, supporting architecture decisions and engineering leadership.

Nov 2025 – Present Current
LiberWerk
Advisory Jan 2026 – Present
Independent Researcher Nov 2025 – Present

Engineering leadership advisory and independent research through my own practice. CTO-as-a-Service, VP of Engineering consulting, and startup technical advisory.

May 2023 – Nov 2025
THECOO Inc.
Chief Technology Officer Jan 2025 – Nov 2025
Head of Engineering Division Aug 2024 – Nov 2025
Senior Engineering Manager Jan 2024 – Sep 2025
Engineering Manager May 2023 – Dec 2023

Progressed from Engineering Manager to CTO over 2.5 years. As CTO and Head of Engineering, oversaw ~40 employees across Product Engineering, Product Management, SRE, Corporate Engineering, QA, and New Product divisions.

May 2022 – Apr 2023
Circle Internet Services, Inc. (CircleCI)
Solutions Engineer May 2022 – Apr 2023

Led CI/CD design and process improvement with enterprise companies across APAC. Drove technical pre-sales and customer integrations.

Apr 2019 – May 2022
Mercari, Inc.
Senior Software Engineer Aug 2021 – May 2022
Software Engineer Apr 2019 – Aug 2021

Designed and built microservices for an 8M+ DAU platform. Migrated PHP monolith to Go/gRPC. Presented at GopherCon and gRPC Conf. Led internal engineering training programmes.

Mar 2018 – Jul 2018
Eventacular Inc.
Software Engineer (Intern) Mar 2018 – Jul 2018

Developed web service frontend with React.js/Relay and backend with Phoenix (Elixir) and GraphQL.

Advisor Profile

Who I Am

Mark Hahn
Mark Hahn Engineering Advisor · Tokyo

I am a trilingual engineering leader based in Japan with hands-on experience scaling a C2C platform to 9.5M+ daily active users, growing engineering organisations 4–5×, and leading ~50 engineers as CTO — across B2B, C2C, and B2B2C product environments.

Through LiberWerk, I channel that experience into advisory engagements — helping founders and engineering leaders scale teams, modernise engineering culture, and build organisations that ship with speed and reliability.

My approach is direct and practical: I bring the pattern recognition from having actually done it — not generic consulting playbooks.

Leadership & Org Scaling

IC → CTO across multiple companies. Grew engineering orgs 4–5×, managed ~50 direct and indirect reports, built hiring and performance frameworks from scratch.

Architecture & Reliability

Designed and scaled systems from 10K to 500K+ users. Microservices, Go/gRPC, SLO/SRE practices, CI/CD — built for real production scale.

Culture & Internationalisation

Transformed High Context Japanese engineering culture to Low Context international standards — English-first documentation, modern dev processes, cross-cultural team building across JP/KR/global.

Go / Golang Microservices gRPC / Protobuf SRE / SLO DevOps / CI/CD Org Design Engineering Strategy B2B · C2C · B2B2C Internationalisation Cross-cultural Teams
Education
Master of Engineering
Tokyo Institute of Technology
2017 – 2019
Bachelor of Science, Computer Science
Dongguk University, Seoul
– 2016
Languages
EN English (British)
JP 日本語
KR 한국어
Based in
Tokyo, Japan
Let's Talk

Start an Engagement

Whether you need a fractional CTO, a technical advisor, or a sounding board for engineering strategy — I'd be glad to hear from you.

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