IoStoreLoaderMod (UE4SS)

IoStoreLoaderMod is a native UE4SS C++ mod that enables loading IoStore-based assets (.pak / .utoc / .ucas) at runtime for Hi-Fi-RUSH, including mods packaged as:

• IoStore-only containers (.utoc + .ucas*)
• Pak-only containers (.pak)
• Full containers (.pak + .utoc + .ucas*)

It mounts containers once the game's normal pak mounting has run, then (optionally) spawns a Blueprint mod actor for each mounted container when the game's PlayerController begins play (HbkPlayerControllerBP_C.ReceiveBeginPlay).

Features

• ✅ Runtime mounting of IoStore containers (.utoc / .ucas)
• ✅ Runtime mounting of Pak containers, including automatic IoStore environment mounting
• ✅ Priority-based mount order (override control)
• ✅ Supports mods with multiple IoStore containers per folder
• ✅ Blueprint ModActor auto-spawn

Requirements

• UE4SS 3.0.1 (C++ mods enabled)
• Mods must be properly cooked for the Hi-FI RUSH (i.e. UE 4.27, IoStore enabled)

Installation

1) Install UE4SS

This mod requires UE4SS version 3.0.1 (⚠ other UE4SS versions are not supported and may not work correctly).

• Download UE4SS v3.0.1 from the official UE4SS releases
• Install UE4SS into the game directory (C:\Program Files (x86)\Steam\steamapps\common\Hi-Fi RUSH\Hibiki\Binaries\Win64)
• Make sure UE4SS is working before continuing
• ❗ Add Hi-Fi RUSH support (if you haven't done it already) by copying UE4SS_Signatures and UE4SS-settings.ini into the game directory.

2) Install IoStoreLoaderMod

1. Copy the mod folder into:

Mods/IoStoreLoaderMod/

Required structure:

Mods/
  IoStoreLoaderMod/
    dlls/
      main.dll

3. Enable the mod in Mods/mods.txt (put it at the very top):

IoStoreLoaderMod : 1

Make sure the name exactly matches the mod folder name.

Where to place your mods

Each mod is a folder inside Mods/IoStoreLoaderMod/:

Mods/
  IoStoreLoaderMod/
    dlls/
      main.dll
    FooMod/
      FooMod.pak
      FooMod.utoc
      FooMod.ucas
    BarMod/
      BarMod.pak
      BarMod.utoc
      BarMod.ucas

• The folder name is used only for sorting / grouping.
• What actually mounts are the container files inside the folder.

Mount Order & Override Rules

When does mounting happen?

IoStoreLoaderMod waits until the game calls Unreal's MountAllPakFiles once.
After that first call completes, it mounts user mods one time.

How are mod folders ordered?

1. It scans all subfolders in Mods/IoStoreLoaderMod/ (excluding dlls/).
2. It sorts folders alphabetically.
3. Each folder is assigned a base mount order order_base = 200 + folder_index.

How are files ordered inside a folder?

• If the folder contains any .pak files:
• All .pak files in that folder are mounted (sorted alphabetically by filename)
• Each one gets:

order = order_base + pak_index

• Otherwise, if there are no .pak files but there are .utoc files:
• All .utoc files are mounted (sorted alphabetically by filename)
• Each one gets:

order = order_base + utoc_index

Who "wins" if two mods replace the same asset?

Higher mount order overrides lower mount order.

Practical rule:

• Folders later in the alphabet mount later (higher order) -> override earlier folders.
• Within the same folder, later file names override earlier file names.

Example:

• A_Mod\aaa.pak mounts before A_Mod\zzz.pak
• Z_Mod\something.pak mounts after both -> overrides both

---

Blueprint Mod Spawning (ModActor)

IoStoreLoaderMod can auto-spawn a Blueprint entry actor for each mounted container.

When does spawning happen?

Spawning is triggered when HbkPlayerControllerBP_C.ReceiveBeginPlay is called.

What gets spawned?

For each mounted container, the loader queues a class path:

/Game/Mods/<BaseName>/ModActor.ModActor_C

Where <BaseName> is derived from the container filename, not the folder name:

• For .pak files:
  • SomeName.pak -> <BaseName> = SomeName
• For .utoc files:
  • Intended: SomeName.utoc-> <BaseName> = SomeName

So if you ship ExampleMod.pak, the loader will try to spawn:

/Game/Mods/ExampleMod/ModActor.ModActor_C

Blueprint custom events

The mod also "implements" the following custom events (duplicated from BPModLoaderMod):

• HbkPrintToModLoader - print to the console
• HbkConstructPersistentObject- create a persistent object

Troubleshooting

Mod does not mount

• Check UE4SS logs
• Verify load_order.txt path is correct
• Ensure the mod is cooked for the same engine version (4.27) with UseIoStore enabled
• Confirm <BaseName> matches the container filename (e.g. ExampleMod.pak -> ExampleMod)
• Remember: Live View shows loaded objects; the class won't appear until it's actually loaded/spawned.

Disclaimer

This mod performs runtime hooks and memory patching. It is intended for modding and research purposes only.

Use at your own risk.