OT6 — Octopath Traveler mechanics in Final Fantasy VI

A mechanics-overhaul ROM hack of Final Fantasy VI (SNES, US "FF3" ROM). It keeps FF6's cast, story, and world, and replaces the combat system with Octopath Traveler's: per-character job identities, shield/break tactics, and a boost-point turn economy.

Status

v0.26 is the current release (tag); this housekeeping release improves the Phantom Train fight, boosted damage, Special weapon weaknesses and boosted Magicite (details in the release notes). The game is playable from the start through the end of the World of Balance: the whole Thamasa arc, the world tour aboard the repaired Blackjack, the IAF gauntlet, the Floating Continent and AtmaWeapon, and the escape — and into the World of Ruin as far as the Falcon, with Setzer back and Darill's Tomb cleared.

Main is v0.27 development; the latest published release is v0.26.

Break and boost are the two central systems. Enemies carry shields and hidden weaknesses, hitting a weakness chips a shield, and breaking drops defenses hard. Boost banks turns and folds spell tiers (Fire → Fira → Firaga). Magicite work as sub-jobs: equip an esper and its spells join your Magic list, along with a stat bump, while you hold it — in battle and in the field menu. Blitz is a menu, Steal guarantees the rare at three boost pips, and level-ups fully restore HP and MP.

See docs/DESIGN.md for the mechanics design and docs/TOOLING.md for tool installation.

Playing on Android

Each release carries ot6-vX.Y.apk, OT6 Patcher: a small app that makes OT6.sfc from your own ROM and keeps it current. To get updates without lifting a finger, subscribe in Obtainium:

1. Add an app with the URL https://github.com/mtklein/ot6, and under "Filter APKs by regular expression" enter ot6-.*\.apk.
2. Install it, open OT6 Patcher once, and choose the folder that holds your own Final Fantasy III (USA) v1.0 ROM (it's never included, and never changed). The app finds the ROM there and writes OT6.sfc beside it. If it can't find it, it lists what it checked, and you can pick the ROM file yourself.
3. From then on, each update Obtainium installs quietly rewrites OT6.sfc, with no notifications; open the app any time to see the last result.

OT6.sfc keeps its name across updates, so your saves and save states carry over. RetroArch: put the ROM in a folder its playlist scans, and re-scan once so OT6.sfc shows up. If you used to soft-patch, delete the Final Fantasy III (USA).bps beside your vanilla ROM so vanilla stays vanilla, and keep any OT6.bps (or .ips, .ups, .xdelta, or a numbered one like OT6.ips1) out of OT6.sfc's folder, since RetroArch would apply it on top; the app warns if it sees one.

Contributing

See AGENTS.md.

Building

You supply your own ROM; it is not included. The build verifies it by SHA-1 and refuses anything else: Final Fantasy III (USA).sfc, sha1 4f37e4274ac3b2ea1bedb08aa149d8fc5bb676e7, at the repo root.

brew bundle                 # cc65, sdl2, ninja, ffmpeg
python3 -m pip install numpy
python3 configure.py        # writes build.ninja
ninja                       # builds and tests everything (qualification)
ninja release               # ...then the release preflights and the zip

Mesen and Flips are not brew-installable; docs/TOOLING.md has those steps.

ninja runs the whole graph: both ROMs, every generated savestate (the story-chain fixtures are multi-minute scripted playthroughs; a cold build takes upward of an hour and a half), all 94 suite tests, the audits and selftests. ninja release adds the release preflights and packaging. Anything narrower is a real output path:

ninja ff6/rom/ff6-en.sfc                    # just the ROM
ninja build/results/suite/battle_break.ok   # one suite test (and what it needs)
ninja build/states/vargas_entry.mss.lua     # one savestate (and its chain)

tools/gui.sh opens the built ROM in the Mesen GUI. OT6_RECORD=1 tools/tests/run.sh tools/tests/<test>.lua records a run as a watchable video with a pad-input panel; see tools/stream/README.md.

Where the code is

OT6 code lives in feature modules emitted from ff6/src/battle/ot6.asm into expanded bank $F0; ot6_memory.inc owns the shared WRAM/SRAM map. ff6/ is a vendored copy of the everything8215/ff6 disassembly (GPL-3.0). The headless play harness is docs/playing-headless.md; tools/tests/README.md covers the test harness.

A warning about Sketch

Relm's Sketch carries Final Fantasy VI 1.0's most famous bug, deliberately left in place: when a Sketch misses, the game can rarely corrupt your inventory or save. Save before experimenting with Sketch; the world map saves anywhere.

License

OT6's own code is MIT (see LICENSE). The Final Fantasy VI disassembly under ff6/ is GPL v3, and so are the built ROM and release patch that include it.