diff --git a/include/constants/pokemon.h b/include/constants/pokemon.h
index 51ef0c015b..a6b150e9e0 100644
--- a/include/constants/pokemon.h
+++ b/include/constants/pokemon.h
@@ -181,6 +181,7 @@
 #define MON_DATA_SPEED2            86
 #define MON_DATA_SPATK2            87
 #define MON_DATA_SPDEF2            88
+#define MON_DATA_NATURE            89
 
 // Ribbon IDs used by TV and Pokénav
 #define CHAMPION_RIBBON       0
diff --git a/src/pokemon.c b/src/pokemon.c
index b4eb6f01af..da3b80baf0 100644
--- a/src/pokemon.c
+++ b/src/pokemon.c
@@ -3980,6 +3980,9 @@ u32 GetBoxMonData(struct BoxPokemon *boxMon, s32 field, u8 *data)
                 | (substruct3->worldRibbon << 26);
         }
         break;
+    case MON_DATA_NATURE:
+        return boxMon->personality % 25;
+        break;
     default:
         break;
     }
@@ -4032,6 +4035,10 @@ void SetMonData(struct Pokemon *mon, s32 field, const void *dataArg)
         break;
     case MON_DATA_SPECIES2:
         break;
+    case MON_DATA_NATURE: // Calculate stats after settings
+        SetBoxMonData(&mon->box, field, data);
+        CalculateMonStats(mon);
+        break;
     default:
         SetBoxMonData(&mon->box, field, data);
         break;
@@ -4298,6 +4305,81 @@ void SetBoxMonData(struct BoxPokemon *boxMon, s32 field, const void *dataArg)
         substruct3->spDefenseIV = (ivs >> 25) & MAX_IV_MASK;
         break;
     }
+    case MON_DATA_NATURE:
+    {
+      u32 pid = boxMon->personality;
+      u32 otId = boxMon->otId;
+      s8 diff = (data[0] % 25) - (pid % 25); // difference between new nature and current nature, [-24,24]
+      bool8 preserveShiny = FALSE;
+      bool8 preserveLetter = FALSE;
+      u16 shinyValue = HIHALF(pid) ^ LOHALF(pid);
+      s32 tweak;
+      u32 pidTemp;
+      // See https://bulbapedia.bulbagarden.net/wiki/Personality_value#Nature
+      // Goal here is to preserve as much of the PID as possible
+      // To preserve gender & substruct order, we add/subtract multiples of 5376 that is 0 % 256, 0 % 24, 1 % 25
+      // i.e, to increase the nature by n % 25, we add n*5376 % 19200 (LCM of 24, 25, 256) to the pid
+      // Ability number is determined by parity and so adding multiples of 5376 preserves it
+      // TODO: For genderless pokemon, 576/600 can be used instead of 5376/19200
+      if (diff == 0) // No change
+        break;
+      else if (diff < 0)
+        diff = 25+diff;
+      tweak = (diff*5376) % 19200;
+      pidTemp = pid + tweak;
+      // If the pokemon is shiny or if changing the PID would make it shiny, preserve its shiny value
+      if (IsShinyOtIdPersonality(otId, pid) || IsShinyOtIdPersonality(otId, pidTemp))
+        preserveShiny = TRUE;
+      if (substruct0->species == SPECIES_UNOWN) // Preserve Unown letter
+        preserveLetter = TRUE;
+      if (preserveShiny && preserveLetter) { // honestly though, how many shiny Unown are out there ?
+        while (pidTemp > pid) {
+          if ((HIHALF(pidTemp) ^ LOHALF(pidTemp) ^ shinyValue) < SHINY_ODDS)
+            if (GET_UNOWN_LETTER(pidTemp) == GET_UNOWN_LETTER(pid))
+              break;
+          pidTemp += 19200;
+        }
+      } else if (preserveShiny) {
+        while (pidTemp > pid) {
+          if ((HIHALF(pidTemp) ^ LOHALF(pidTemp) ^ shinyValue) < SHINY_ODDS)
+            break;
+          pidTemp += 19200;
+        }
+      } else if (preserveLetter) {
+        while (pidTemp > pid) {
+          if (GET_UNOWN_LETTER(pidTemp) == GET_UNOWN_LETTER(pid))
+            break;
+          pidTemp += 19200;
+        }
+      }
+      if (pidTemp < pid) { // overflow; search backwards
+        tweak -= 19200;
+        pidTemp = pid + tweak;
+        if (preserveShiny && preserveLetter) {
+          while (pidTemp < pid) {
+            if ((HIHALF(pidTemp) ^ LOHALF(pidTemp) ^ shinyValue) < SHINY_ODDS)
+              if (GET_UNOWN_LETTER(pidTemp) == GET_UNOWN_LETTER(pid))
+                break;
+            pidTemp -= 19200;
+          }
+        } else if (preserveShiny) {
+          while (pidTemp < pid) {
+            if ((HIHALF(pidTemp) ^ LOHALF(pidTemp) ^ shinyValue) < SHINY_ODDS)
+              break;
+            pidTemp -= 19200;
+          }
+        } else if (preserveLetter) {
+          while (pidTemp < pid) {
+            if (GET_UNOWN_LETTER(pidTemp) == GET_UNOWN_LETTER(pid))
+              break;
+            pidTemp -= 19200;
+          }
+        }
+      }
+      if (pid % 24 == pidTemp % 24 || pid % 256 == pidTemp % 256)
+        boxMon->personality = pidTemp;
+      break;
+    }
     default:
         break;
     }
@@ -4878,7 +4960,7 @@ bool8 PokemonUseItemEffects(struct Pokemon *mon, u16 item, u8 partyIndex, u8 mov
                         temp2 = itemEffect[itemEffectParam];
                         dataSigned = GetMonData(mon, sGetMonDataEVConstants[temp1], NULL);
                         evChange = temp2;
-     
+
                         if (evChange > 0) // Increasing EV (HP or Atk)
                         {
                             // Has EV increase limit already been reached?
@@ -4976,7 +5058,7 @@ bool8 PokemonUseItemEffects(struct Pokemon *mon, u16 item, u8 partyIndex, u8 mov
                         {
                             if (!usedByAI)
                             {
-                                // Restore HP 
+                                // Restore HP
                                 dataUnsigned = GetMonData(mon, MON_DATA_HP, NULL) + dataUnsigned;
                                 if (dataUnsigned > GetMonData(mon, MON_DATA_MAX_HP, NULL))
                                     dataUnsigned = GetMonData(mon, MON_DATA_MAX_HP, NULL);
@@ -5055,7 +5137,7 @@ bool8 PokemonUseItemEffects(struct Pokemon *mon, u16 item, u8 partyIndex, u8 mov
                                     dataUnsigned = CalculatePPWithBonus(moveId, GetMonData(mon, MON_DATA_PP_BONUSES, NULL), moveIndex);
                                 }
                                 SetMonData(mon, MON_DATA_PP1 + moveIndex, &dataUnsigned);
-                                
+
                                 // Heal battler PP too (if applicable)
                                 if (gMain.inBattle
                                  && battlerId != MAX_BATTLERS_COUNT && !(gBattleMons[battlerId].status2 & STATUS2_TRANSFORMED)
@@ -5092,7 +5174,7 @@ bool8 PokemonUseItemEffects(struct Pokemon *mon, u16 item, u8 partyIndex, u8 mov
         case 5:
             effectFlags = itemEffect[i];
             temp1 = 0;
-            
+
             // Loop through and try each of the ITEM5 effects
             while (effectFlags != 0)
             {