diff --git a/SVSim.EmulatedEntrypoint/Matching/AIBotProfile.cs b/SVSim.EmulatedEntrypoint/Matching/AIBotProfile.cs
new file mode 100644
index 0000000..70b2ee8
--- /dev/null
+++ b/SVSim.EmulatedEntrypoint/Matching/AIBotProfile.cs
@@ -0,0 +1,23 @@
+namespace SVSim.EmulatedEntrypoint.Matching;
+
+/// <summary>
+/// Cosmetic + identity metadata for an AI opponent. Used to compose
+/// <c>oppo_info</c> in the <c>/ai_&lt;fmt&gt;_rank_battle/start</c> response.
+/// The wire keys are camelCase (sleeveId, emblemId, etc.) — the DTO handles
+/// the JSON serialization; this record is the internal-facing shape.
+/// </summary>
+public sealed record AIBotProfile(
+    int AiId,
+    string CountryCode,
+    string UserName,
+    int SleeveId,
+    int EmblemId,
+    int DegreeId,
+    int FieldId,
+    int IsOfficial,
+    int ClassId,
+    int CharaId,
+    int Rank,
+    int BattlePoint,
+    int IsMasterRank,
+    int MasterPoint);
diff --git a/SVSim.EmulatedEntrypoint/Matching/BotRoster.cs b/SVSim.EmulatedEntrypoint/Matching/BotRoster.cs
new file mode 100644
index 0000000..486f08e
--- /dev/null
+++ b/SVSim.EmulatedEntrypoint/Matching/BotRoster.cs
@@ -0,0 +1,55 @@
+using SVSim.BattleNode.Bridge;
+
+namespace SVSim.EmulatedEntrypoint.Matching;
+
+/// <summary>
+/// Phase 3 hardcoded fixture: one stub bot per class (1..8). <c>ai_id</c>
+/// values 4001..4008 are placeholders per the existing
+/// <c>docs/api-spec/endpoints/post-login/rank-battle/ai-start.md</c> TODO —
+/// no live capture exists to validate the real prod catalog.
+/// </summary>
+public sealed class BotRoster : IBotRoster
+{
+    // Cosmetic ids (sleeve / emblem / degree / field) intentionally use safe
+    // default values that match the master tables shipped in the project.
+    // The client-side AI catalog reads ai_id but renders cosmetics from the
+    // sleeveId/emblemId/etc returned here.
+    private static readonly IReadOnlyList<AIBotProfile> Roster = new[]
+    {
+        new AIBotProfile(AiId: 4001, CountryCode: "NONE", UserName: "Forestcraft AI",
+            SleeveId: 1001, EmblemId: 1, DegreeId: 1, FieldId: 1, IsOfficial: 0,
+            ClassId: 1, CharaId: 1, Rank: 10, BattlePoint: 0, IsMasterRank: 0, MasterPoint: 0),
+        new AIBotProfile(AiId: 4002, CountryCode: "NONE", UserName: "Swordcraft AI",
+            SleeveId: 1001, EmblemId: 1, DegreeId: 1, FieldId: 1, IsOfficial: 0,
+            ClassId: 2, CharaId: 2, Rank: 10, BattlePoint: 0, IsMasterRank: 0, MasterPoint: 0),
+        new AIBotProfile(AiId: 4003, CountryCode: "NONE", UserName: "Runecraft AI",
+            SleeveId: 1001, EmblemId: 1, DegreeId: 1, FieldId: 1, IsOfficial: 0,
+            ClassId: 3, CharaId: 3, Rank: 10, BattlePoint: 0, IsMasterRank: 0, MasterPoint: 0),
+        new AIBotProfile(AiId: 4004, CountryCode: "NONE", UserName: "Dragoncraft AI",
+            SleeveId: 1001, EmblemId: 1, DegreeId: 1, FieldId: 1, IsOfficial: 0,
+            ClassId: 4, CharaId: 4, Rank: 10, BattlePoint: 0, IsMasterRank: 0, MasterPoint: 0),
+        new AIBotProfile(AiId: 4005, CountryCode: "NONE", UserName: "Shadowcraft AI",
+            SleeveId: 1001, EmblemId: 1, DegreeId: 1, FieldId: 1, IsOfficial: 0,
+            ClassId: 5, CharaId: 5, Rank: 10, BattlePoint: 0, IsMasterRank: 0, MasterPoint: 0),
+        new AIBotProfile(AiId: 4006, CountryCode: "NONE", UserName: "Bloodcraft AI",
+            SleeveId: 1001, EmblemId: 1, DegreeId: 1, FieldId: 1, IsOfficial: 0,
+            ClassId: 6, CharaId: 6, Rank: 10, BattlePoint: 0, IsMasterRank: 0, MasterPoint: 0),
+        new AIBotProfile(AiId: 4007, CountryCode: "NONE", UserName: "Havencraft AI",
+            SleeveId: 1001, EmblemId: 1, DegreeId: 1, FieldId: 1, IsOfficial: 0,
+            ClassId: 7, CharaId: 7, Rank: 10, BattlePoint: 0, IsMasterRank: 0, MasterPoint: 0),
+        new AIBotProfile(AiId: 4008, CountryCode: "NONE", UserName: "Portalcraft AI",
+            SleeveId: 1001, EmblemId: 1, DegreeId: 1, FieldId: 1, IsOfficial: 0,
+            ClassId: 8, CharaId: 8, Rank: 10, BattlePoint: 0, IsMasterRank: 0, MasterPoint: 0),
+    };
+
+    public AIBotProfile Pick(MatchContext selfCtx)
+    {
+        // Deterministic: hash the ctx and pick from the roster. Same ctx →
+        // same bot so a mid-flight retry of /ai_<fmt>/start returns the same
+        // opponent (no fresh roster pick on each call).
+        var hash = StringComparer.Ordinal.GetHashCode(selfCtx.UserName)
+            ^ StringComparer.Ordinal.GetHashCode(selfCtx.ClassId);
+        var index = (int)((uint)hash % Roster.Count);
+        return Roster[index];
+    }
+}
diff --git a/SVSim.EmulatedEntrypoint/Matching/IBotRoster.cs b/SVSim.EmulatedEntrypoint/Matching/IBotRoster.cs
new file mode 100644
index 0000000..e5348ad
--- /dev/null
+++ b/SVSim.EmulatedEntrypoint/Matching/IBotRoster.cs
@@ -0,0 +1,21 @@
+using SVSim.BattleNode.Bridge;
+
+namespace SVSim.EmulatedEntrypoint.Matching;
+
+/// <summary>
+/// Picks a bot opponent for an incoming AI rank battle. Used by
+/// <c>RankBattleController.AiStart</c> to compose <c>oppo_info</c>.
+/// </summary>
+/// <remarks>
+/// Phase 3 ships a hardcoded fixture; future improvement is to migrate the roster
+/// to <c>SVSim.Bootstrap/Data/seeds/bot-roster.json</c> for editability without
+/// rebuilds. See spec § Future improvements.
+/// </remarks>
+public interface IBotRoster
+{
+    /// <summary>
+    /// Returns a bot profile for the calling viewer. Deterministic per
+    /// <see cref="MatchContext"/> — the same context value returns the same bot.
+    /// </summary>
+    AIBotProfile Pick(MatchContext selfCtx);
+}
diff --git a/SVSim.EmulatedEntrypoint/Program.cs b/SVSim.EmulatedEntrypoint/Program.cs
index 2c927e7..0824e34 100644
--- a/SVSim.EmulatedEntrypoint/Program.cs
+++ b/SVSim.EmulatedEntrypoint/Program.cs
@@ -138,6 +138,8 @@ public class Program
             new ModePolicy("unlimited_rank_battle", PolicyKind.PvpFirstThenAiFallback),
         }));
         builder.Services.AddSingleton<IMatchingPairUpService, InProcessPairUp>();
+        // Phase 3: bot fixture used by RankBattleController.AiStart to compose oppo_info.
+        builder.Services.AddSingleton<IBotRoster, BotRoster>();
 
         builder.Services.AddTransient<ShadowverseTranslationMiddleware>();
         builder.Services.AddTransient<SessionidMappingMiddleware>();
diff --git a/SVSim.UnitTests/Matching/BotRosterTests.cs b/SVSim.UnitTests/Matching/BotRosterTests.cs
new file mode 100644
index 0000000..7efee8d
--- /dev/null
+++ b/SVSim.UnitTests/Matching/BotRosterTests.cs
@@ -0,0 +1,48 @@
+using NUnit.Framework;
+using SVSim.BattleNode.Bridge;
+using SVSim.EmulatedEntrypoint.Matching;
+
+namespace SVSim.UnitTests.Matching;
+
+[TestFixture]
+public class BotRosterTests
+{
+    private static MatchContext Ctx(string userName, string classId) => new(
+        SelfDeckCardIds: Array.Empty<long>(),
+        ClassId: classId, CharaId: classId, CardMasterName: "card_master_node_10015",
+        CountryCode: "JP", UserName: userName, SleeveId: "0",
+        EmblemId: "0", DegreeId: "0", FieldId: 0, IsOfficial: 0, BattleType: 11);
+
+    [Test]
+    public void Pick_returns_a_bot_with_valid_ai_id()
+    {
+        var roster = new BotRoster();
+        var bot = roster.Pick(Ctx("PlayerA", "1"));
+
+        Assert.That(bot.AiId, Is.InRange(4001, 4008));
+    }
+
+    [Test]
+    public void Pick_returns_bot_with_class_metadata_set()
+    {
+        var roster = new BotRoster();
+        var bot = roster.Pick(Ctx("PlayerA", "1"));
+
+        Assert.That(bot.ClassId, Is.InRange(1, 8));
+        Assert.That(bot.CharaId, Is.InRange(1, 8));
+        Assert.That(bot.UserName, Is.Not.Null.And.Not.Empty);
+        Assert.That(bot.CountryCode, Is.EqualTo("NONE"));
+    }
+
+    [Test]
+    public void Pick_is_deterministic_per_match_context()
+    {
+        var roster = new BotRoster();
+        var ctx = Ctx("PlayerA", "3");
+
+        var a = roster.Pick(ctx);
+        var b = roster.Pick(ctx);
+
+        Assert.That(a, Is.EqualTo(b), "Same ctx → same bot, so mid-flight retries get the same opponent.");
+    }
+}