From ca6fbf024c6616a07026266ee33c0ddbb5d5a46a Mon Sep 17 00:00:00 2001
From: Kurt <kwsch@users.noreply.github.com>
Date: Thu, 19 Mar 2026 03:20:42 -0500
Subject: [PATCH] Add new virtual method for pre-applying Nickname

Results in correct trash bytes for user-Nickname'd mons as if they were nicknamed via the in-game menu.
---
 PKHeX.Core/Editing/CommonEdits.cs                     |  4 +++-
 .../Legality/RNG/Methods/Gen9/GenerateParam9.cs       |  2 +-
 PKHeX.Core/Legality/Verifiers/Misc/MiscVerifierG3.cs  |  6 +++---
 PKHeX.Core/PKM/PK3.cs                                 | 11 +++++++++++
 PKHeX.Core/PKM/PKM.cs                                 |  5 +++++
 5 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/PKHeX.Core/Editing/CommonEdits.cs b/PKHeX.Core/Editing/CommonEdits.cs
index a7a12539c..f8ffade9c 100644
--- a/PKHeX.Core/Editing/CommonEdits.cs
+++ b/PKHeX.Core/Editing/CommonEdits.cs
@@ -30,8 +30,10 @@ public void SetNickname(string nick)
                 pk.ClearNickname();
                 return;
             }
-            pk.IsNicknamed = true;
+
+            pk.PrepareNickname();
             pk.Nickname = nick;
+            pk.IsNicknamed = true;
         }
 
         /// <summary>
diff --git a/PKHeX.Core/Legality/RNG/Methods/Gen9/GenerateParam9.cs b/PKHeX.Core/Legality/RNG/Methods/Gen9/GenerateParam9.cs
index 1d191f097..3e4f16043 100644
--- a/PKHeX.Core/Legality/RNG/Methods/Gen9/GenerateParam9.cs
+++ b/PKHeX.Core/Legality/RNG/Methods/Gen9/GenerateParam9.cs
@@ -4,7 +4,7 @@ namespace PKHeX.Core;
 /// Parameters used to generate data for an encounter.
 /// </summary>
 /// <param name="Species">Species to generate.</param>
-/// <param name="GenderRatio">Gender ratio byte.</param>
+/// <param name="GenderRatio">Gender ratio byte from Personal Info.</param>
 /// <param name="FlawlessIVs">Count of IVs that are perfect.</param>
 /// <param name="RollCount">Count of shiny rolls allowed for the PID calculation.</param>
 /// <param name="Height">Height value to generate. If zero, full random.</param>
diff --git a/PKHeX.Core/Legality/Verifiers/Misc/MiscVerifierG3.cs b/PKHeX.Core/Legality/Verifiers/Misc/MiscVerifierG3.cs
index 0edae4e67..d6f4f062d 100644
--- a/PKHeX.Core/Legality/Verifiers/Misc/MiscVerifierG3.cs
+++ b/PKHeX.Core/Legality/Verifiers/Misc/MiscVerifierG3.cs
@@ -135,9 +135,9 @@ private static void FlagIsNicknameClean(LegalityAnalysis data, PK3 pk)
     {
         if (!pk.IsNicknamed || pk.IsEgg)
             return;
-        var nick = pk.NicknameTrash;
-        if (pk.Japanese)
-            nick = nick[..5]; // Japanese only wipes the first 5 bytes; everything else is trash.
+        // Japanese only fills the first 5+1 bytes; everything else is trash.
+        // International games are 10 chars (full buffer) max; implicit terminator if full.
+        var nick = pk.GetNicknamePrefillRegion();
         if (!TrashByteRules3.IsTerminatedFF(nick))
             data.AddLine(GetInvalid(Trainer, TrashBytesMismatchInitial));
     }
diff --git a/PKHeX.Core/PKM/PK3.cs b/PKHeX.Core/PKM/PK3.cs
index 578ab6793..e36b551d4 100644
--- a/PKHeX.Core/PKM/PK3.cs
+++ b/PKHeX.Core/PKM/PK3.cs
@@ -398,4 +398,15 @@ public override int GetStringTerminatorIndex(ReadOnlySpan<byte> data)
     public override int GetStringLength(ReadOnlySpan<byte> data)
         => TrashBytes8.GetStringLength(data);
     public override int GetBytesPerChar() => 1;
+
+    public override void PrepareNickname() => GetNicknamePrefillRegion().Fill(StringConverter3.TerminatorByte);
+
+    public Span<byte> GetNicknamePrefillRegion()
+    {
+        // Japanese only fills the first 5+1 bytes; everything else is trash.
+        // International games are 10 chars (full buffer) max; implicit terminator if full.
+        if (Japanese)
+            return NicknameTrash[..6];
+        return NicknameTrash;
+    }
 }
diff --git a/PKHeX.Core/PKM/PKM.cs b/PKHeX.Core/PKM/PKM.cs
index 612ba34d3..0d538c050 100644
--- a/PKHeX.Core/PKM/PKM.cs
+++ b/PKHeX.Core/PKM/PKM.cs
@@ -44,6 +44,11 @@ public abstract class PKM : ISpeciesForm, ITrainerID32, IGeneration, IShiny, ILa
     public abstract Span<byte> OriginalTrainerTrash { get; }
     public virtual Span<byte> HandlingTrainerTrash => [];
 
+    /// <summary>
+    /// Conditions the <see cref="NicknameTrash"/> data to safely terminate the Nickname string from the text entry screen.
+    /// </summary>
+    public virtual void PrepareNickname() { }
+
     protected abstract byte[] Encrypt();
     public abstract EntityContext Context { get; }
     public byte Format => Context.Generation;