diff --git a/README.md b/README.md
index 20b43bd..283a172 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # Chiisai Event Emitter
 
-A minimal event emitter library for Node.JS.
+A minimal and performant event emitter library for Node.JS.
 
 ---
 
@@ -14,8 +14,6 @@ A minimal event emitter library for Node.JS.
 [![Commitizen Friendly][commitizen-img]][commitizen-url]
 [![Semantic Release][semantic-release-img]][semantic-release-url]
 
-> My awesome module
-
 ## Install
 
 ```bash
@@ -25,32 +23,17 @@ npm install chiisai-event-emitter
 ## Usage
 
 ```ts
-import { myPackage } from 'chiisai-event-emitter';
-
-myPackage('hello');
-//=> 'hello from my package'
-```
-
-## API
-
-### myPackage(input, options?)
-
-#### input
+import eventEmitter from 'chiisai-event-emitter';
 
-Type: `string`
+const eventEmitter = new EventEmitter();
 
-Lorem ipsum.
+eventEmitter.subscribe('test-event', () => console.log('test-event handler called!'));
+eventEmitter.subscribe('test-event', () => console.log('another test-event handler called!'))
 
-#### options
-
-Type: `object`
-
-##### postfix
-
-Type: `string`
-Default: `rainbows`
-
-Lorem ipsum.
+eventEmitter.emit('test-event')
+// test-event handler called!
+// another test-event handler called!
+```
 
 [build-img]:https://github.com/ryansonshine/chiisai-event-emitter/actions/workflows/release.yml/badge.svg
 [build-url]:https://github.com/ryansonshine/chiisai-event-emitter/actions/workflows/release.yml
diff --git a/src/index.ts b/src/index.ts
index 0349cbc..73b5d11 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1 +1,49 @@
-export const myPackage = (taco = ''): string => `${taco} from my package`;
+export type EventCallback<T = void> = (...args: Array<any>) => T;
+export type Subscriptions = Map<
+  string,
+  Array<{ id: symbol; callback: EventCallback }>
+>;
+export type Unsubscribe = { unsubscribe: () => void };
+
+export class EventEmitter {
+  subscriptions: Subscriptions;
+
+  constructor() {
+    this.subscriptions = new Map();
+  }
+
+  /**
+   * @param {string} eventName
+   * @param {EventCallback} callback
+   * @return {Unsubscribe}
+   */
+  subscribe(eventName: string, callback: EventCallback): Unsubscribe {
+    const id = Symbol(callback.toString());
+    this.subscriptions.set(
+      eventName,
+      this.subscriptions.has(eventName)
+        ? [...(this.subscriptions.get(eventName) || []), { id, callback }]
+        : [{ id, callback }]
+    );
+
+    return {
+      unsubscribe: () =>
+        this.subscriptions.set(
+          eventName,
+          (this.subscriptions.get(eventName) || []).filter(
+            ({ id: subscriptionId }) => subscriptionId !== id
+          )
+        ),
+    };
+  }
+
+  /**
+   * @param {string} eventName
+   * @param {Array<any>} args
+   */
+  emit(eventName: string, args: Array<any> = []): void {
+    (this.subscriptions.get(eventName) || []).forEach(({ callback }) =>
+      callback(...args)
+    );
+  }
+}