diff --git a/src/c2se/backend/identity.rs b/src/c2se/backend/identity.rs
index f8cd7d5..5febeeb 100644
--- a/src/c2se/backend/identity.rs
+++ b/src/c2se/backend/identity.rs
@@ -2,20 +2,6 @@ use crate::protobuf::rpc;
 
 const SUBJECT: &str = "bet.beteran.c2se.backend.identity";
 
-pub const SUBJECT_CAPTCHA: &str = const_format::concatcp!(SUBJECT, ".Captcha");
-/// subject = bet.beteran.c2se.backend.identity.Captcha
-#[derive(Clone, PartialEq, ::prost::Message)]
-pub struct CaptchaRequest {}
-#[derive(Clone, PartialEq, ::prost::Message)]
-pub struct CaptchaResponse {
-  #[prost(message, optional, tag = "1")]
-  pub error: ::core::option::Option<rpc::Error>,
-  #[prost(string, optional, tag = "2")]
-  pub token: ::core::option::Option<::prost::alloc::string::String>,
-  #[prost(string, optional, tag = "3")]
-  pub image: ::core::option::Option<::prost::alloc::string::String>,
-}
-
 pub const SUBJECT_SIGNIN: &str = const_format::concatcp!(SUBJECT, ".Signin");
 /// subject = bet.beteran.c2se.backend.identity.Signin
 #[derive(Clone, PartialEq, ::prost::Message)]
diff --git a/src/c2se/backend/mod.rs b/src/c2se/backend/mod.rs
index cf7a71d..f764bbb 100644
--- a/src/c2se/backend/mod.rs
+++ b/src/c2se/backend/mod.rs
@@ -1 +1,2 @@
-pub mod identity;
\ No newline at end of file
+pub mod identity;
+pub mod member;
diff --git a/src/c2se/common/identity.rs b/src/c2se/common/identity.rs
new file mode 100644
index 0000000..a858973
--- /dev/null
+++ b/src/c2se/common/identity.rs
@@ -0,0 +1,52 @@
+use crate::protobuf::rpc;
+
+const SUBJECT: &str = "bet.beteran.c2se.common.identity";
+
+pub const SUBJECT_CHECK_USERNAME_FOR_DUPLICATION: &str =
+  const_format::concatcp!(SUBJECT, ".CheckUsernameForDuplication");
+/// subject = bet.beteran.c2se.common.identity.CheckUsernameForDuplication;
+#[derive(Clone, PartialEq, ::prost::Message)]
+pub struct CheckUsernameForDuplicationRequest {
+  #[prost(string, tag = "1")]
+  pub username: ::prost::alloc::string::String,
+}
+
+#[derive(Clone, PartialEq, ::prost::Message)]
+pub struct CheckUsernameForDuplicationResponse {
+  #[prost(message, optional, tag = "1")]
+  pub error: ::core::option::Option<rpc::Error>,
+  #[prost(bool, optional, tag = "2")]
+  pub duplicated: ::core::option::Option<bool>,
+}
+
+pub const SUBJECT_CHECK_NICKNAME_FOR_DUPLICATION: &str =
+  const_format::concatcp!(SUBJECT, ".CheckNicknameForDuplication");
+/// subject = bet.beteran.c2se.common.identity.CheckNicknameForDuplication;
+#[derive(Clone, PartialEq, ::prost::Message)]
+pub struct CheckNicknameForDuplicationRequest {
+  #[prost(string, tag = "1")]
+  pub nickname: ::prost::alloc::string::String,
+}
+
+#[derive(Clone, PartialEq, ::prost::Message)]
+pub struct CheckNicknameForDuplicationResponse {
+  #[prost(message, optional, tag = "1")]
+  pub error: ::core::option::Option<rpc::Error>,
+  #[prost(bool, optional, tag = "2")]
+  pub duplicated: ::core::option::Option<bool>,
+}
+
+pub const SUBJECT_CAPTCHA: &str = const_format::concatcp!(SUBJECT, ".Captcha");
+/// subject = bet.beteran.c2se.common.identity.Captcha
+#[derive(Clone, PartialEq, ::prost::Message)]
+pub struct CaptchaRequest {}
+
+#[derive(Clone, PartialEq, ::prost::Message)]
+pub struct CaptchaResponse {
+  #[prost(message, optional, tag = "1")]
+  pub error: ::core::option::Option<rpc::Error>,
+  #[prost(string, optional, tag = "2")]
+  pub token: ::core::option::Option<::prost::alloc::string::String>,
+  #[prost(string, optional, tag = "3")]
+  pub image: ::core::option::Option<::prost::alloc::string::String>,
+}
diff --git a/src/c2se/common/mod.rs b/src/c2se/common/mod.rs
new file mode 100644
index 0000000..db53a0c
--- /dev/null
+++ b/src/c2se/common/mod.rs
@@ -0,0 +1 @@
+pub mod identity;
diff --git a/src/c2se/frontend/identity.rs b/src/c2se/frontend/identity.rs
index f80faed..35372f5 100644
--- a/src/c2se/frontend/identity.rs
+++ b/src/c2se/frontend/identity.rs
@@ -2,20 +2,6 @@ use crate::protobuf::rpc;
 
 const SUBJECT: &str = "bet.beteran.c2se.frontend.identity";
 
-pub const SUBJECT_CAPTCHA: &str = const_format::concatcp!(SUBJECT, ".Captcha");
-/// subject = bet.beteran.c2se.frontend.identity.Captcha
-#[derive(Clone, PartialEq, ::prost::Message)]
-pub struct CaptchaRequest {}
-#[derive(Clone, PartialEq, ::prost::Message)]
-pub struct CaptchaResponse {
-  #[prost(message, optional, tag = "1")]
-  pub error: ::core::option::Option<rpc::Error>,
-  #[prost(string, optional, tag = "2")]
-  pub token: ::core::option::Option<::prost::alloc::string::String>,
-  #[prost(string, optional, tag = "3")]
-  pub image: ::core::option::Option<::prost::alloc::string::String>,
-}
-
 pub const SUBJECT_SIGNIN: &str = const_format::concatcp!(SUBJECT, ".Signin");
 /// subject = bet.beteran.c2se.frontend.identity.Signin
 #[derive(Clone, PartialEq, ::prost::Message)]
@@ -29,6 +15,7 @@ pub struct SigninRequest {
   #[prost(string, tag = "4")]
   pub password: ::prost::alloc::string::String,
 }
+
 #[derive(Clone, PartialEq, ::prost::Message)]
 pub struct SigninResponse {
   #[prost(message, optional, tag = "1")]
diff --git a/src/c2se/mod.rs b/src/c2se/mod.rs
index 5290bd1..9ad44dc 100644
--- a/src/c2se/mod.rs
+++ b/src/c2se/mod.rs
@@ -4,6 +4,7 @@
 ///
 pub mod backend;
 ///
+pub mod common;
 ///
 pub mod core;
 ///
diff --git a/src/ss/member/identity.rs b/src/ss/member/identity.rs
index e8385a4..1375ca6 100644
--- a/src/ss/member/identity.rs
+++ b/src/ss/member/identity.rs
@@ -3,6 +3,42 @@ use crate::protobuf::rpc;
 
 const SUBJECT: &str = "bet.beteran.ss.member.identity";
 
+pub const SUBJECT_CHECK_USERNAME_FOR_DUPLICATION: &str =
+  const_format::concatcp!(SUBJECT, ".CheckUsernameForDuplication");
+/// subject = bet.beteran.ss.member.identity.CheckUsernameForDuplication;
+#[derive(Clone, PartialEq, ::prost::Message)]
+pub struct CheckUsernameForDuplicationRequest {
+  #[prost(message, optional, tag = "1")]
+  pub client: ::core::option::Option<core::network::Client>,
+  #[prost(string, tag = "2")]
+  pub username: ::prost::alloc::string::String,
+}
+#[derive(Clone, PartialEq, ::prost::Message)]
+pub struct CheckUsernameForDuplicationResponse {
+  #[prost(message, optional, tag = "1")]
+  pub error: ::core::option::Option<rpc::Error>,
+  #[prost(bool, optional, tag = "2")]
+  pub duplicated: ::core::option::Option<bool>,
+}
+
+pub const SUBJECT_CHECK_NICKNAME_FOR_DUPLICATION: &str =
+  const_format::concatcp!(SUBJECT, ".CheckNicknameForDuplication");
+/// subject = bet.beteran.ss.member.identity.CheckNicknameForDuplication;
+#[derive(Clone, PartialEq, ::prost::Message)]
+pub struct CheckNicknameForDuplicationRequest {
+  #[prost(message, optional, tag = "1")]
+  pub client: ::core::option::Option<core::network::Client>,
+  #[prost(string, tag = "2")]
+  pub nickname: ::prost::alloc::string::String,
+}
+#[derive(Clone, PartialEq, ::prost::Message)]
+pub struct CheckNicknameForDuplicationResponse {
+  #[prost(message, optional, tag = "1")]
+  pub error: ::core::option::Option<rpc::Error>,
+  #[prost(bool, optional, tag = "2")]
+  pub duplicated: ::core::option::Option<bool>,
+}
+
 pub const SUBJECT_CAPTCHA: &str = const_format::concatcp!(SUBJECT, ".Captcha");
 /// subject = bet.beteran.ss.member.identity.Captcha
 #[derive(Clone, PartialEq, ::prost::Message)]