diff --git a/index.d.ts b/index.d.ts
index c92cda02..34f3a733 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -1,3 +1,4 @@
+import type { PartialTuple } from 'spica/type';
 import { Observer } from 'spica/observation';
 import { AtomicPromise } from 'spica/promise';
 import { ChannelObject } from './index';
@@ -7,9 +8,9 @@ export { ChannelObject } from './index';
 export class StoreChannel<K extends string, V extends StoreChannelObject<K>> {
   constructor(name: string, config: StoreChannelConfig<K, V>);
   readonly events: {
-    readonly load: Observer<[K] | [K, Extract<keyof V | '', string>] | [K, Extract<keyof V | '', string>, StoreChannelEventType], StoreChannelEvent<K, V>, void>;
-    readonly save: Observer<[K] | [K, Extract<keyof V | '', string>] | [K, Extract<keyof V | '', string>, StoreChannelEventType], StoreChannelEvent<K, V>, void>;
-    readonly loss: Observer<[K] | [K, Extract<keyof V | '', string>] | [K, Extract<keyof V | '', string>, StoreChannelEventType], StoreChannelEvent<K, V>, void>;
+    readonly load: Observer<PartialTuple<[K, Extract<keyof V | '', string>, StoreChannelEventType]>, StoreChannelEvent<K, V>, void>;
+    readonly save: Observer<PartialTuple<[K, Extract<keyof V | '', string>, StoreChannelEventType]>, StoreChannelEvent<K, V>, void>;
+    readonly loss: Observer<PartialTuple<[K, Extract<keyof V | '', string>, StoreChannelEventType]>, StoreChannelEvent<K, V>, void>;
   };
   sync(keys: K[], cb?: (results: AtomicPromise<K>[]) => void): void;
   link(key: K, age?: number): V;
@@ -30,7 +31,7 @@ export interface StoreChannelObject<K extends string> {
   readonly [ChannelObject.id]: number;
   readonly [ChannelObject.key]: K;
   readonly [ChannelObject.date]: number;
-  readonly [ChannelObject.event]: Observer<[StorageChannelEventType] | [StorageChannelEventType, Extract<keyof this, string>], StorageChannelEvent<this>, void>;
+  readonly [ChannelObject.event]: Observer<PartialTuple<[StorageChannelEventType, Extract<keyof this, string>]>, StorageChannelEvent<this>, void>;
 }
 export interface StoreChannelObjectMetaData<K extends string> {
   readonly id: number;
@@ -68,7 +69,7 @@ export interface StorageChannelConfig<V extends StorageChannelObject> {
   migrate?(link: V): void;
 }
 export interface StorageChannelObject {
-  readonly [ChannelObject.event]: Observer<[StorageChannelEventType] | [StorageChannelEventType, Extract<keyof this, string>], StorageChannelEvent<this>, void>;
+  readonly [ChannelObject.event]: Observer<PartialTuple<[StorageChannelEventType, Extract<keyof this, string>]>, StorageChannelEvent<this>, void>;
 }
 export interface StorageChannelEvent<V> {
   readonly type: StorageChannelEventType;
diff --git a/package.json b/package.json
index b75b9df6..2fb76939 100644
--- a/package.json
+++ b/package.json
@@ -61,7 +61,7 @@
     "npm-check-updates": "^4.0.1",
     "power-assert": "^1.6.1",
     "semver": "^7.1.1",
-    "spica": "0.0.313",
+    "spica": "0.0.314",
     "tsify": "^4.0.1",
     "typescript": "3.8.0-dev.20200125",
     "vinyl-buffer": "^1.0.1",
diff --git a/src/layer/data/es/store.ts b/src/layer/data/es/store.ts
index dc50a702..4c4d27b1 100644
--- a/src/layer/data/es/store.ts
+++ b/src/layer/data/es/store.ts
@@ -1,3 +1,4 @@
+import type { PartialTuple } from 'spica/type';
 import { Observation } from 'spica/observation';
 import { Cancellation } from 'spica/cancellation';
 import { tick } from 'spica/clock';
@@ -98,15 +99,15 @@ export abstract class EventStore<K extends string, V extends EventStore.Value> {
         }
       });
   }
-  private readonly memory = new Observation<[] | [K] | [K, keyof V | ''] | [K, keyof V | '', string] | [K, keyof V | '', string, string], void, UnstoredEventRecord<K, V> | LoadedEventRecord<K, V> | SavedEventRecord<K, V>>();
+  private readonly memory = new Observation<PartialTuple<[K, keyof V | '', string, string]>, void, UnstoredEventRecord<K, V> | LoadedEventRecord<K, V> | SavedEventRecord<K, V>>();
   public readonly events = Object.freeze({
-    load: new Observation<[K] | [K, Extract<keyof V | '', string>] | [K, Extract<keyof V | '', string>, EventStore.EventType], EventStore.Event<K, V>, void>(),
-    save: new Observation<[K] | [K, Extract<keyof V | '', string>] | [K, Extract<keyof V | '', string>, EventStore.EventType], EventStore.Event<K, V>, void>(),
-    loss: new Observation<[K] | [K, Extract<keyof V | '', string>] | [K, Extract<keyof V | '', string>, EventStore.EventType], EventStore.Event<K, V>, void>(),
+    load: new Observation<PartialTuple<[K, Extract<keyof V | '', string>, EventStore.EventType]>, EventStore.Event<K, V>, void>(),
+    save: new Observation<PartialTuple<[K, Extract<keyof V | '', string>, EventStore.EventType]>, EventStore.Event<K, V>, void>(),
+    loss: new Observation<PartialTuple<[K, Extract<keyof V | '', string>, EventStore.EventType]>, EventStore.Event<K, V>, void>(),
     clean: new Observation<[K], boolean, void>(),
   });
   private readonly events_ = Object.freeze({
-    memory: new Observation<[K] | [K, keyof V | ''] | [K, keyof V | '', string], UnstoredEventRecord<K, V> | LoadedEventRecord<K, V> | SavedEventRecord<K, V>, void>({ limit: Infinity }),
+    memory: new Observation<PartialTuple<[K, keyof V | '', string]>, UnstoredEventRecord<K, V> | LoadedEventRecord<K, V> | SavedEventRecord<K, V>, void>({ limit: Infinity }),
   });
   private tx_: {
     rw?: IDBTransaction;
diff --git a/src/layer/domain/indexeddb/model/channel.ts b/src/layer/domain/indexeddb/model/channel.ts
index 593953ca..015174a4 100644
--- a/src/layer/domain/indexeddb/model/channel.ts
+++ b/src/layer/domain/indexeddb/model/channel.ts
@@ -1,4 +1,5 @@
 import { StoreChannelObject, StoreChannelObjectMetaData } from '../../../../../';
+import type { PartialTuple } from 'spica/type';
 import { Observation } from 'spica/observation';
 import { Cancellation } from 'spica/cancellation';
 import { AtomicPromise } from 'spica/promise';
@@ -135,14 +136,14 @@ export class ChannelStore<K extends string, V extends StoreChannelObject<K>> {
     };
   })(), { ignore: { delete: true } });
   public readonly events_ = Object.freeze({
-    load: new Observation<[K] | [K, keyof V | ''] | [K, keyof V | '', ChannelStore.EventType], ChannelStore.Event<K, V>, void>(),
-    save: new Observation<[K] | [K, keyof V | ''] | [K, keyof V | '', ChannelStore.EventType], ChannelStore.Event<K, V>, void>(),
+    load: new Observation<PartialTuple<[K, keyof V | '', ChannelStore.EventType]>, ChannelStore.Event<K, V>, void>(),
+    save: new Observation<PartialTuple<[K, keyof V | '', ChannelStore.EventType]>, ChannelStore.Event<K, V>, void>(),
     clean: new Observation<[K], boolean, void>(),
   });
   public readonly events = Object.freeze({
-    load: new Observation<[K] | [K, Extract<keyof V | '', string>] | [K, Extract<keyof V | '', string>, ChannelStore.EventType], ChannelStore.Event<K, V>, void>({ limit: Infinity }),
-    save: new Observation<[K] | [K, Extract<keyof V | '', string>] | [K, Extract<keyof V | '', string>, ChannelStore.EventType], ChannelStore.Event<K, V>, void>({ limit: Infinity }),
-    loss: new Observation<[K] | [K, Extract<keyof V | '', string>] | [K, Extract<keyof V | '', string>, ChannelStore.EventType], ChannelStore.Event<K, V>, void>({ limit: Infinity }),
+    load: new Observation<PartialTuple<[K, Extract<keyof V | '', string>, ChannelStore.EventType]>, ChannelStore.Event<K, V>, void>({ limit: Infinity }),
+    save: new Observation<PartialTuple<[K, Extract<keyof V | '', string>, ChannelStore.EventType]>, ChannelStore.Event<K, V>, void>({ limit: Infinity }),
+    loss: new Observation<PartialTuple<[K, Extract<keyof V | '', string>, ChannelStore.EventType]>, ChannelStore.Event<K, V>, void>({ limit: Infinity }),
   });
   public sync(keys: K[], cb: (results: AtomicPromise<K>[]) => void = noop, timeout = Infinity): void {
     const cancellation = new Cancellation();
diff --git a/src/layer/domain/indexeddb/service/channel.ts b/src/layer/domain/indexeddb/service/channel.ts
index cb0d762b..4a27fab3 100644
--- a/src/layer/domain/indexeddb/service/channel.ts
+++ b/src/layer/domain/indexeddb/service/channel.ts
@@ -56,6 +56,7 @@ export class StoreChannel<K extends string, V extends StoreChannelObject<K>> ext
           if (changes.length === 0) return;
           void migrate(link);
           for (const { attr, oldVal } of changes) {
+            // @ts-ignore #31251
             void cast(source[Schema.event]!)
               .emit([StorageChannel.EventType.recv, attr], new StorageChannel.Event<V>(StorageChannel.EventType.recv, attr as never, memory[attr as never], oldVal as never));
           }
@@ -97,6 +98,7 @@ export class StoreChannel<K extends string, V extends StoreChannelObject<K>> ext
           () => this.factory(),
           (attr, newValue, oldValue) => (
             void this.add(new ChannelStore.Record<K, V>(key, { [attr]: newValue } as Partial<V>)),
+            // @ts-ignore #31251
             void cast(this.sources.get(key)![Schema.event]!)
               .emit([StorageChannel.EventType.send, attr], new StorageChannel.Event<V>(StorageChannel.EventType.send, attr as never, newValue, oldValue))),
           throttle(100, () => this.has(key) && void this.log(key))))