diff --git a/composer.json b/composer.json
index 02284dba1d..ccde4f890e 100644
--- a/composer.json
+++ b/composer.json
@@ -47,7 +47,8 @@
         "pear/xml_util": "*",
         "setasign/fpdf": "^1.8",
         "setasign/fpdi": "^2.6",
-        "smarty/smarty": "^5.0.2"
+        "smarty/smarty": "^5.0.2",
+        "symfony/polyfill-php80": "^1.31"
     },
     "autoload": {
         "classmap": [
diff --git a/composer.lock b/composer.lock
index 615706a368..4171b3c24d 100644
--- a/composer.lock
+++ b/composer.lock
@@ -899,6 +899,86 @@
                 }
             ],
             "time": "2024-09-09T11:45:10+00:00"
+        },
+        {
+            "name": "symfony/polyfill-php80",
+            "version": "v1.31.0",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/symfony/polyfill-php80.git",
+                "reference": "60328e362d4c2c802a54fcbf04f9d3fb892b4cf8"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/symfony/polyfill-php80/zipball/60328e362d4c2c802a54fcbf04f9d3fb892b4cf8",
+                "reference": "60328e362d4c2c802a54fcbf04f9d3fb892b4cf8",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=7.2"
+            },
+            "type": "library",
+            "extra": {
+                "thanks": {
+                    "name": "symfony/polyfill",
+                    "url": "https://github.com/symfony/polyfill"
+                }
+            },
+            "autoload": {
+                "files": [
+                    "bootstrap.php"
+                ],
+                "psr-4": {
+                    "Symfony\\Polyfill\\Php80\\": ""
+                },
+                "classmap": [
+                    "Resources/stubs"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Ion Bazan",
+                    "email": "ion.bazan@gmail.com"
+                },
+                {
+                    "name": "Nicolas Grekas",
+                    "email": "p@tchwork.com"
+                },
+                {
+                    "name": "Symfony Community",
+                    "homepage": "https://symfony.com/contributors"
+                }
+            ],
+            "description": "Symfony polyfill backporting some PHP 8.0+ features to lower PHP versions",
+            "homepage": "https://symfony.com",
+            "keywords": [
+                "compatibility",
+                "polyfill",
+                "portable",
+                "shim"
+            ],
+            "support": {
+                "source": "https://github.com/symfony/polyfill-php80/tree/v1.31.0"
+            },
+            "funding": [
+                {
+                    "url": "https://symfony.com/sponsor",
+                    "type": "custom"
+                },
+                {
+                    "url": "https://github.com/fabpot",
+                    "type": "github"
+                },
+                {
+                    "url": "https://tidelift.com/funding/github/packagist/symfony/symfony",
+                    "type": "tidelift"
+                }
+            ],
+            "time": "2024-09-09T11:45:10+00:00"
         }
     ],
     "packages-dev": [
@@ -5092,86 +5172,6 @@
             ],
             "time": "2024-09-09T11:45:10+00:00"
         },
-        {
-            "name": "symfony/polyfill-php80",
-            "version": "v1.31.0",
-            "source": {
-                "type": "git",
-                "url": "https://github.com/symfony/polyfill-php80.git",
-                "reference": "60328e362d4c2c802a54fcbf04f9d3fb892b4cf8"
-            },
-            "dist": {
-                "type": "zip",
-                "url": "https://api.github.com/repos/symfony/polyfill-php80/zipball/60328e362d4c2c802a54fcbf04f9d3fb892b4cf8",
-                "reference": "60328e362d4c2c802a54fcbf04f9d3fb892b4cf8",
-                "shasum": ""
-            },
-            "require": {
-                "php": ">=7.2"
-            },
-            "type": "library",
-            "extra": {
-                "thanks": {
-                    "name": "symfony/polyfill",
-                    "url": "https://github.com/symfony/polyfill"
-                }
-            },
-            "autoload": {
-                "files": [
-                    "bootstrap.php"
-                ],
-                "psr-4": {
-                    "Symfony\\Polyfill\\Php80\\": ""
-                },
-                "classmap": [
-                    "Resources/stubs"
-                ]
-            },
-            "notification-url": "https://packagist.org/downloads/",
-            "license": [
-                "MIT"
-            ],
-            "authors": [
-                {
-                    "name": "Ion Bazan",
-                    "email": "ion.bazan@gmail.com"
-                },
-                {
-                    "name": "Nicolas Grekas",
-                    "email": "p@tchwork.com"
-                },
-                {
-                    "name": "Symfony Community",
-                    "homepage": "https://symfony.com/contributors"
-                }
-            ],
-            "description": "Symfony polyfill backporting some PHP 8.0+ features to lower PHP versions",
-            "homepage": "https://symfony.com",
-            "keywords": [
-                "compatibility",
-                "polyfill",
-                "portable",
-                "shim"
-            ],
-            "support": {
-                "source": "https://github.com/symfony/polyfill-php80/tree/v1.31.0"
-            },
-            "funding": [
-                {
-                    "url": "https://symfony.com/sponsor",
-                    "type": "custom"
-                },
-                {
-                    "url": "https://github.com/fabpot",
-                    "type": "github"
-                },
-                {
-                    "url": "https://tidelift.com/funding/github/packagist/symfony/symfony",
-                    "type": "tidelift"
-                }
-            ],
-            "time": "2024-09-09T11:45:10+00:00"
-        },
         {
             "name": "symfony/polyfill-php81",
             "version": "v1.31.0",
diff --git a/data/class/SC_Initial.php b/data/class/SC_Initial.php
index bc50ded1fc..95ca067ace 100644
--- a/data/class/SC_Initial.php
+++ b/data/class/SC_Initial.php
@@ -57,7 +57,6 @@ public function init()
         $this->resetSuperglobalsRequest();  // stripslashesDeepGpc メソッドより後で実行
         $this->setTimezone();               // 本当はエラーハンドラーより先に読みたい気も
         $this->normalizeHostname();         // defineConstants メソッドより後で実行
-        $this->compatPhp();
     }
 
     /**
@@ -549,46 +548,4 @@ public function normalizeHostname()
             SC_Response_Ex::sendRedirect($correct_url);
         }
     }
-
-    /**
-     * PHPバージョン互換処理
-     *
-     * @deprecated https://github.com/EC-CUBE/ec-cube2/issues/681 が実現したら、外部ライブラリへ移行して、削除する予定。
-     *
-     * @return void
-     */
-    public function compatPhp()
-    {
-        if (!function_exists('str_starts_with')) {
-            /**
-             * 文字列が指定された部分文字列で始まるかを調べる。(for PHP < 8)
-             *
-             * @param string $haystack
-             * @param string $needle
-             *
-             * @return bool
-             */
-            function str_starts_with($haystack, $needle)
-            {
-                return strncmp($haystack, $needle, strlen($needle)) === 0;
-            }
-        }
-
-        if (!function_exists('str_ends_with')) {
-            /**
-             * 文字列が、指定された文字列で終わるかを調べる。(for PHP < 8)
-             *
-             * @param string $haystack
-             * @param string $needle
-             *
-             * @return bool
-             */
-            function str_ends_with($haystack, $needle)
-            {
-                $needle_len = strlen($needle);
-
-                return substr($haystack, -$needle_len, $needle_len) === $needle;
-            }
-        }
-    }
 }
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
index 2e1b6745f2..fedf1b2161 100644
--- a/phpstan.neon.dist
+++ b/phpstan.neon.dist
@@ -38,9 +38,6 @@ parameters:
     -
       message: "#^Variable \\$SJIS_widths might not be defined\\.$#"
       path: data/class/helper/SC_Helper_FPDI.php
-    -
-      message: "#^Inner named functions are not supported by PHPStan\\.#"
-      path: data/class/SC_Initial.php
     -
       message: '#^Path in include_once\(\) "Auth/SASL.php" is not a file or it does not exist.#'
       path: data/module/Net/SMTP.php