diff --git a/filesystem/system_other.go b/filesystem/system_other.go
new file mode 100644
index 0000000..cad4263
--- /dev/null
+++ b/filesystem/system_other.go
@@ -0,0 +1,122 @@
+// Copyright (C) 2024 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package filesystem
+
+import (
+	"android/soong/android"
+	"path/filepath"
+	"strings"
+
+	"github.com/google/blueprint"
+	"github.com/google/blueprint/proptools"
+)
+
+type SystemOtherImageProperties struct {
+	// The system_other image always requires a reference to the system image. The system_other
+	// partition gets built into the system partition's "b" slot in a/b partition builds. Thus, it
+	// copies most of its configuration from the system image, such as filesystem type, avb signing
+	// info, etc. Including it here does not automatically mean that it will pick up the system
+	// image's dexpropt files, it must also be listed in Preinstall_dexpreopt_files_from for that.
+	System_image *string
+
+	// This system_other partition will include all the dexpreopt files from the apps on these
+	// partitions.
+	Preinstall_dexpreopt_files_from []string
+}
+
+type systemOtherImage struct {
+	android.ModuleBase
+	android.DefaultableModuleBase
+	properties SystemOtherImageProperties
+}
+
+// The system_other image is the default contents of the "b" slot of the system image.
+// It contains the dexpreopt files of all the apps on the device, for a faster first boot.
+// Afterwards, at runtime, it will be used as a regular b slot for OTA updates, and the initial
+// dexpreopt files will be deleted.
+func SystemOtherImageFactory() android.Module {
+	module := &systemOtherImage{}
+	module.AddProperties(&module.properties)
+	android.InitAndroidMultiTargetsArchModule(module, android.DeviceSupported, android.MultilibCommon)
+	android.InitDefaultableModule(module)
+	return module
+}
+
+type systemImageDeptag struct {
+	blueprint.BaseDependencyTag
+}
+
+var systemImageDependencyTag = systemImageDeptag{}
+
+type dexpreoptDeptag struct {
+	blueprint.BaseDependencyTag
+}
+
+var dexpreoptDependencyTag = dexpreoptDeptag{}
+
+func (m *systemOtherImage) DepsMutator(ctx android.BottomUpMutatorContext) {
+	if proptools.String(m.properties.System_image) == "" {
+		ctx.ModuleErrorf("system_image property must be set")
+		return
+	}
+	ctx.AddDependency(ctx.Module(), systemImageDependencyTag, *m.properties.System_image)
+	ctx.AddDependency(ctx.Module(), dexpreoptDependencyTag, m.properties.Preinstall_dexpreopt_files_from...)
+}
+
+func (m *systemOtherImage) GenerateAndroidBuildActions(ctx android.ModuleContext) {
+	systemImage := ctx.GetDirectDepProxyWithTag(*m.properties.System_image, systemImageDependencyTag)
+	systemInfo, ok := android.OtherModuleProvider(ctx, systemImage, FilesystemProvider)
+	if !ok {
+		ctx.PropertyErrorf("system_image", "Expected system_image module to provide FilesystemProvider")
+		return
+	}
+
+	output := android.PathForModuleOut(ctx, "system_other.img")
+	stagingDir := android.PathForModuleOut(ctx, "staging_dir")
+
+	builder := android.NewRuleBuilder(pctx, ctx)
+	builder.Command().Textf("rm -rf %s && mkdir -p %s", stagingDir, stagingDir)
+
+	for _, otherPartition := range m.properties.Preinstall_dexpreopt_files_from {
+		dexModule := ctx.GetDirectDepProxyWithTag(otherPartition, dexpreoptDependencyTag)
+		_, ok := android.OtherModuleProvider(ctx, dexModule, FilesystemProvider)
+		if !ok {
+			ctx.PropertyErrorf("preinstall_dexpreopt_files_from", "Expected module %q to provide FilesystemProvider", otherPartition)
+			return
+		}
+		// TODO(b/390269431): Install dex files to the staging dir
+	}
+
+	// Most of the time, if build_image were to call a host tool, it accepts the path to the
+	// host tool in a field in the prop file. However, it doesn't have that option for fec, which
+	// it expects to just be on the PATH. Add fec to the PATH.
+	fec := ctx.Config().HostToolPath(ctx, "fec")
+	pathToolDirs := []string{filepath.Dir(fec.String())}
+
+	builder.Command().
+		Textf("PATH=%s:$PATH", strings.Join(pathToolDirs, ":")).
+		BuiltTool("build_image").
+		Text(stagingDir.String()). // input directory
+		Input(systemInfo.BuildImagePropFile).
+		Implicits(systemInfo.BuildImagePropFileDeps).
+		Implicit(fec).
+		Output(output).
+		Text(stagingDir.String())
+
+	builder.Build("build_system_other", "build system other")
+
+	ctx.SetOutputFiles(android.Paths{output}, "")
+	ctx.CheckbuildFile(output)
+}