yep

Shogi.Api/Controllers/SessionsController.cs

@@ -39,7 +39,7 @@ public class SessionsController : ControllerBase
 	public async Task<IActionResult> CreateSession([FromBody] CreateSessionCommand request)
 	{
 		var userId = User.GetShogiUserId();
-		var session = new Domain.Aggregates.Session(request.Name, userId);
+		var session = new Domain.Session(request.Name, userId);
 		try
 		{
 			await sessionRepository.CreateSession(session);
@@ -126,7 +126,7 @@ public class SessionsController : ControllerBase
 			}
 			else
 			{
-				session.Board.Move(command.From!, command.To, command.IsPromotion);
+				session.Board.Move(command.From!, command.To, command.IsPromotion!.Value);
 			}
 		}
 		catch (InvalidOperationException)

Shogi.Api/Extensions/ContractsExtensions.cs

@@ -50,6 +50,7 @@ public static class ContractsExtensions
 	public static Dictionary<string, Piece?> ToContract(this ReadOnlyDictionary<string, Domain.ValueObjects.Piece?> boardState) =>
 		boardState.ToDictionary(kvp => kvp.Key, kvp => kvp.Value?.ToContract());
 
+	public static Domain.WhichPiece? ToDomain(this WhichPiece? piece) => piece.HasValue ? piece.Value.ToDomain() : null;
 	public static Domain.WhichPiece ToDomain(this WhichPiece piece)
 	{
 		return piece switch

Shogi.Api/Repositories/Dto/MoveDto.cs

@@ -5,6 +5,6 @@ namespace Shogi.Api.Repositories.Dto;
 /// <summary>
 /// Useful with Dapper to read from database.
 /// </summary>
-public readonly record struct MoveDto(string From, string To, bool IsPromotion, WhichPiece? PieceFromHand)
+public readonly record struct MoveDto(string? From, string To, bool? IsPromotion, WhichPiece? PieceFromHand)
 {
 }

Shogi.Api/Repositories/SessionRepository.cs

@@ -1,6 +1,7 @@
 using Dapper;
+using Shogi.Api.Extensions;
 using Shogi.Api.Repositories.Dto;
-using Shogi.Domain.Aggregates;
+using Shogi.Domain;
 using System.Data;
 using System.Data.SqlClient;
 
@@ -65,6 +66,15 @@ public class SessionRepository : ISessionRepository
 		}
 		return session;
 	}
+
+	public async Task CreateMove(string sessionName, Contracts.Api.MovePieceCommand command)
+	{
+		using var connection = new SqlConnection(connectionString);
+		await connection.ExecuteAsync(
+			"session.CreateMove",
+			new { },
+			commandType: CommandType.StoredProcedure);
+	}
 }
 
 public interface ISessionRepository

Shogi.Contracts/Api/Commands/MovePieceCommand.cs

@@ -7,6 +7,33 @@ namespace Shogi.Contracts.Api;
 
 public class MovePieceCommand : IValidatableObject
 {
+	/// <summary>
+	/// For serialization.
+	/// </summary>
+	public MovePieceCommand()
+	{
+		To = string.Empty;
+	}
+
+	/// <summary>
+	/// Move a piece on the board.
+	/// </summary>
+	public MovePieceCommand(string from, string to, bool isPromotion)
+	{
+		From = from;
+		To = to;
+		IsPromotion = isPromotion;
+	}
+
+	/// <summary>
+	/// Add a piece to the board from the hand.
+	/// </summary>
+	public MovePieceCommand(WhichPiece pieceFromHand, string to)
+	{
+		PieceFromHand = pieceFromHand;
+		To = to;
+	}
+
 	/// <summary>
 	/// Mutually exclusive with <see cref="From"/>.
 	/// Set this property to indicate moving a piece from the hand onto the board.
@@ -26,7 +53,7 @@ public class MovePieceCommand : IValidatableObject
 	[Required]
 	public string To { get; set; }
 	
-	public bool IsPromotion { get; set; }
+	public bool? IsPromotion { get; set; }
 
 	public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
 	{
@@ -34,6 +61,10 @@ public class MovePieceCommand : IValidatableObject
 		{
 			yield return new ValidationResult($"{nameof(PieceFromHand)} and {nameof(From)} are mutually exclusive properties.");
 		}
+		if (PieceFromHand.HasValue && IsPromotion.HasValue)
+		{
+			yield return new ValidationResult($"{nameof(PieceFromHand)} and {nameof(IsPromotion)} are mutually exclusive properties.");
+		}
 		if (!Regex.IsMatch(To, "[A-I][1-9]"))
 		{
 			yield return new ValidationResult($"{nameof(To)} must be a valid board position, between A1 and I9");

Shogi.Database/Session/Stored Procedures/CreateMove.sql

@@ -0,0 +1,9 @@
+CREATE PROCEDURE [session].[CreateMove]
+	@To					VARCHAR(2),
+	@From				VARCHAR(2),
+	@IsPromotion		BIT,
+	@PieceName			NVARCHAR(13),
+	@SessionName		[session].[SessionName]
+AS
+	SELECT @param1, @param2
+RETURN 0

Shogi.Database/Session/Tables/Move.sql

@@ -2,9 +2,9 @@
 (
 	[Id]				INT NOT NULL PRIMARY KEY IDENTITY,
 	[SessionId]			BIGINT NOT NULL,
-	[From]			VARCHAR(2) NOT NULL,
 	[To]				VARCHAR(2) NOT NULL,
-	[IsPromotion]	BIT NOT NULL,
+	[From]				VARCHAR(2) NULL,
+	[IsPromotion]		BIT NULL,
 	[PieceIdFromHand]	INT NULL
 
 	CONSTRAINT [Cannot end where you start]

Shogi.Database/Shogi.Database.sqlproj

@@ -87,6 +87,7 @@
     <Build Include="Session\Tables\Move.sql" />
     <Build Include="Session\Tables\Piece.sql" />
     <Build Include="Session\Stored Procedures\DeleteSession.sql" />
+    <Build Include="Session\Stored Procedures\CreateMove.sql" />
   </ItemGroup>
   <ItemGroup>
     <PostDeploy Include="Post Deployment\Script.PostDeployment.sql" />

Shogi.Domain/Aggregates/Session.cs

@@ -1,6 +1,6 @@
 using Shogi.Domain.ValueObjects;
 
-namespace Shogi.Domain.Aggregates;
+namespace Shogi.Domain;
 
 public class Session
 {