diff --git a/supabase/migrations/20260123000000_add_characters_variables_to_flowchart_data.sql b/supabase/migrations/20260123000000_add_characters_variables_to_flowchart_data.sql
new file mode 100644
index 0000000..2a0642c
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+++ b/supabase/migrations/20260123000000_add_characters_variables_to_flowchart_data.sql
@@ -0,0 +1,45 @@
+-- Migration: Add characters and variables arrays to flowchart_data JSONB default
+-- Part of Character/Variable Management feature (US-055)
+--
+-- The characters and variables arrays are stored within the flowchart_data JSONB column.
+-- This migration updates the default value for new projects to include empty arrays.
+-- Existing projects without these fields are handled at the application layer,
+-- which defaults missing characters/variables to empty arrays on read.
+
+-- =============================================================================
+-- UPDATE DEFAULT VALUE FOR flowchart_data
+-- =============================================================================
+-- Update the default to include characters and variables arrays
+ALTER TABLE projects
+  ALTER COLUMN flowchart_data
+  SET DEFAULT '{"nodes": [], "edges": [], "characters": [], "variables": []}'::jsonb;
+
+-- =============================================================================
+-- DOCUMENTATION: JSONB Structure
+-- =============================================================================
+-- The flowchart_data column now expects the following top-level structure:
+--
+-- {
+--   "nodes": [...],           -- Array of flowchart nodes
+--   "edges": [...],           -- Array of flowchart edges
+--   "characters": [           -- Array of character definitions
+--     {
+--       "id": "string",         -- Unique identifier (nanoid)
+--       "name": "string",       -- Character name (required, unique per project)
+--       "color": "string",      -- Hex color code (e.g., "#FF5733")
+--       "description": "string" -- Optional description
+--     }
+--   ],
+--   "variables": [            -- Array of variable definitions
+--     {
+--       "id": "string",         -- Unique identifier (nanoid)
+--       "name": "string",       -- Variable name (required, unique per project)
+--       "type": "string",       -- One of: 'numeric', 'string', 'boolean'
+--       "initialValue": "any",  -- Initial value matching the type
+--       "description": "string" -- Optional description
+--     }
+--   ]
+-- }
+--
+-- Note: Existing projects that do not have characters/variables fields
+-- are handled at the application layer, which defaults them to empty arrays.