diff --git a/app/build.gradle.kts b/app/build.gradle.kts
index 853e359f6..664229f5f 100644
--- a/app/build.gradle.kts
+++ b/app/build.gradle.kts
@@ -162,9 +162,11 @@ dependencies {
     implementation("org.conscrypt:conscrypt-android:2.5.2")
 
     // Data serialization (JSON, protobuf)
-    val kotlinSerializationVersion = "1.2.2"
+    val kotlinSerializationVersion = "1.3.0-RC"
     implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:$kotlinSerializationVersion")
     implementation("org.jetbrains.kotlinx:kotlinx-serialization-protobuf:$kotlinSerializationVersion")
+
+    // TODO: remove these once they're no longer used in any extensions
     implementation("com.google.code.gson:gson:2.8.7")
     implementation("com.github.salomonbrys.kotson:kotson:2.5.0")
 
diff --git a/app/src/main/java/eu/kanade/tachiyomi/data/backup/legacy/LegacyBackupRestore.kt b/app/src/main/java/eu/kanade/tachiyomi/data/backup/legacy/LegacyBackupRestore.kt
index 80236da8e..451a589d6 100644
--- a/app/src/main/java/eu/kanade/tachiyomi/data/backup/legacy/LegacyBackupRestore.kt
+++ b/app/src/main/java/eu/kanade/tachiyomi/data/backup/legacy/LegacyBackupRestore.kt
@@ -15,13 +15,12 @@ import eu.kanade.tachiyomi.data.database.models.Track
 import eu.kanade.tachiyomi.source.Source
 import exh.EXHMigrations
 import exh.merged.sql.models.MergedMangaReference
-import kotlinx.serialization.decodeFromString
 import kotlinx.serialization.json.Json
 import kotlinx.serialization.json.JsonObject
 import kotlinx.serialization.json.decodeFromJsonElement
+import kotlinx.serialization.json.decodeFromStream
 import kotlinx.serialization.json.intOrNull
 import kotlinx.serialization.json.jsonPrimitive
-import okio.buffer
 import okio.source
 import java.util.Date
 
@@ -34,8 +33,8 @@ class LegacyBackupRestore(context: Context, notifier: BackupNotifier) : Abstract
 
         // Read the json and create a Json Object,
         // cannot use the backupManager json deserializer one because its not initialized yet
-        val backupObject = Json.decodeFromString<JsonObject>(
-            context.contentResolver.openInputStream(uri)!!.source().buffer().use { it.readUtf8() }
+        val backupObject = Json.decodeFromStream<JsonObject>(
+            context.contentResolver.openInputStream(uri)!!
         )
 
         // Get parser version
diff --git a/app/src/main/java/eu/kanade/tachiyomi/data/backup/legacy/LegacyBackupRestoreValidator.kt b/app/src/main/java/eu/kanade/tachiyomi/data/backup/legacy/LegacyBackupRestoreValidator.kt
index ac6a83bc2..b82544f2a 100644
--- a/app/src/main/java/eu/kanade/tachiyomi/data/backup/legacy/LegacyBackupRestoreValidator.kt
+++ b/app/src/main/java/eu/kanade/tachiyomi/data/backup/legacy/LegacyBackupRestoreValidator.kt
@@ -5,9 +5,7 @@ import android.net.Uri
 import eu.kanade.tachiyomi.R
 import eu.kanade.tachiyomi.data.backup.AbstractBackupRestoreValidator
 import eu.kanade.tachiyomi.data.backup.legacy.models.Backup
-import kotlinx.serialization.decodeFromString
-import okio.buffer
-import okio.source
+import kotlinx.serialization.json.decodeFromStream
 
 class LegacyBackupRestoreValidator : AbstractBackupRestoreValidator() {
     /**
@@ -19,8 +17,8 @@ class LegacyBackupRestoreValidator : AbstractBackupRestoreValidator() {
     override fun validate(context: Context, uri: Uri): Results {
         val backupManager = LegacyBackupManager(context)
 
-        val backup = backupManager.parser.decodeFromString<Backup>(
-            context.contentResolver.openInputStream(uri)!!.source().buffer().use { it.readUtf8() }
+        val backup = backupManager.parser.decodeFromStream<Backup>(
+            context.contentResolver.openInputStream(uri)!!
         )
 
         if (backup.version == null) {
diff --git a/app/src/main/java/eu/kanade/tachiyomi/source/LocalSource.kt b/app/src/main/java/eu/kanade/tachiyomi/source/LocalSource.kt
index 105f0991c..88af8a6cb 100755
--- a/app/src/main/java/eu/kanade/tachiyomi/source/LocalSource.kt
+++ b/app/src/main/java/eu/kanade/tachiyomi/source/LocalSource.kt
@@ -16,15 +16,13 @@ import eu.kanade.tachiyomi.util.storage.DiskUtil
 import eu.kanade.tachiyomi.util.storage.EpubFile
 import eu.kanade.tachiyomi.util.system.ImageUtil
 import kotlinx.serialization.Serializable
-import kotlinx.serialization.decodeFromString
 import kotlinx.serialization.encodeToString
 import kotlinx.serialization.json.Json
-import okio.buffer
-import okio.source
+import kotlinx.serialization.json.decodeFromStream
+import kotlinx.serialization.json.encodeToStream
 import rx.Observable
 import timber.log.Timber
-import uy.kohesive.injekt.Injekt
-import uy.kohesive.injekt.api.get
+import uy.kohesive.injekt.injectLazy
 import java.io.File
 import java.io.FileInputStream
 import java.io.InputStream
@@ -74,14 +72,13 @@ class LocalSource(private val context: Context) : CatalogueSource {
             val c = context.getString(R.string.app_name) + File.separator + "local"
             return DiskUtil.getExternalStorages(context).map { File(it.absolutePath, c) }
         }
-
-        // SY -->
-        val json = Json {
-            prettyPrint = true
-        }
-        // SY <--
     }
 
+    private val json: Json by injectLazy()
+    // SY -->
+    private val preferences: PreferencesHelper by injectLazy()
+    // SY <--
+
     override val id = ID
     override val name = context.getString(R.string.local_source)
     override val lang = ""
@@ -94,7 +91,7 @@ class LocalSource(private val context: Context) : CatalogueSource {
     override fun fetchSearchManga(page: Int, query: String, filters: FilterList): Observable<MangasPage> {
         val baseDirs = getBaseDirectories(context)
         // SY -->
-        val allowLocalSourceHiddenFolders = Injekt.get<PreferencesHelper>().allowLocalSourceHiddenFolders().get()
+        val allowLocalSourceHiddenFolders = preferences.allowLocalSourceHiddenFolders().get()
         // SY <--
 
         val time = if (filters === LATEST_FILTERS) System.currentTimeMillis() - LATEST_THRESHOLD else 0L
@@ -172,7 +169,9 @@ class LocalSource(private val context: Context) : CatalogueSource {
         } ?: return
         val existingFileName = directory.listFiles()?.find { it.extension == "json" }?.name
         val file = File(directory, existingFileName ?: "info.json")
-        file.writeText(json.encodeToString(manga.toJson()))
+        file.outputStream().use {
+            json.encodeToStream(manga.toJson(), it)
+        }
     }
 
     private fun SManga.toJson(): MangaJson {
@@ -199,12 +198,7 @@ class LocalSource(private val context: Context) : CatalogueSource {
             .flatten()
             .firstOrNull { it.extension == "json" }
             ?.apply {
-                val json = json.decodeFromString<MangaJson>(
-                    this.inputStream()
-                        .source()
-                        .buffer()
-                        .use { it.readUtf8() }
-                )
+                val json = json.decodeFromStream<MangaJson>(inputStream())
 
                 manga.title = json.title ?: manga.title
                 manga.author = json.author ?: manga.author