diff --git a/defects/renpy-0001/patch/renpy-0001.patch b/defects/renpy-0001/patch/renpy-0001.patch
new file mode 100644
index 000000000..6c9b95814
--- /dev/null
+++ b/defects/renpy-0001/patch/renpy-0001.patch
@@ -0,0 +1,35 @@
+# UNDF: UNDF-2026-000000969
+--- a/renpy/display/image.py
++++ b/renpy/display/image.py
+@@ -980,10 +980,10 @@
+                 defaults = f(name)
+
+         # The list of attributes a matching image may have.
+-        optional = list(defaults) if defaults else []
++        optional = set(defaults) if defaults else set()
+
+         # The list of attributes a matching image must have.
+-        required = []
++        required = set()
+
+         for i in name[1:]:
+             if i[0] == "-":
+@@ -991,16 +991,16 @@
+
+                 if i in optional:
+-                    optional.remove(i)
++                    optional.discard(i)
+
+                 if i in required:
+-                    required.remove(i)
++                    required.discard(i)
+
+             else:
+-                required.append(i)
++                required.add(i)
+
+         return self.choose_image(nametag, required, optional, name)
+
+     def choose_image(self, tag, required, optional, exception_name):
+         # The longest length of an image that matches.
+         max_len = -1
diff --git a/defects/renpy-0001/test/renpy-0001-test.py b/defects/renpy-0001/test/renpy-0001-test.py
new file mode 100644
index 000000000..9da02dc25
--- /dev/null
+++ b/defects/renpy-0001/test/renpy-0001-test.py
@@ -0,0 +1,119 @@
+#!/usr/bin/env python3
+"""
+Unit test for renpy-0001: ShownImageInfo.choose_image required/optional list
+membership O(I*A*(R+O)) -> set membership O(I*A)
+
+Defect: In renpy/display/image.py, ShownImageInfo.apply_attributes() builds
+`required` and `optional` as Python lists, then passes them to choose_image().
+Inside choose_image(), the inner loop checks `i in required` and `i in optional`
+for every attribute of every registered image for a tag. With lists, each `in`
+check is O(N), making the total O(I * A * (R + O)) where I = images per tag,
+A = attributes per image, R = len(required), O = len(optional).
+
+Fix: Change `required` and `optional` from lists to sets. Membership test
+becomes O(1), total becomes O(I * A). Use set.add/discard instead of
+list.append/remove.
+
+File: renpy/display/image.py
+Method: ShownImageInfo.apply_attributes / ShownImageInfo.choose_image
+Lines: 984-1002 (apply_attributes), 1011-1032 (choose_image inner loop)
+"""
+
+import time
+
+
+def simulate_defective(image_attrs_by_tag, required_list, optional_list):
+    """
+    Simulates choose_image with required and optional as lists.
+    O(I * A * (R + O)) due to list membership checks.
+    """
+    matches = []
+    for attrs in image_attrs_by_tag:
+        if not all((i in required_list) or (i in optional_list) for i in attrs):
+            continue
+        num_required = 0
+        for i in attrs:
+            if i in required_list:
+                num_required += 1
+        if num_required != len(required_list):
+            continue
+        matches.append(attrs)
+    return matches
+
+
+def simulate_fixed(image_attrs_by_tag, required_set, optional_set):
+    """
+    Simulates choose_image with required and optional as sets.
+    O(I * A) due to set membership checks.
+    """
+    matches = []
+    for attrs in image_attrs_by_tag:
+        if not all((i in required_set) or (i in optional_set) for i in attrs):
+            continue
+        num_required = 0
+        for i in attrs:
+            if i in required_set:
+                num_required += 1
+        if num_required != len(required_set):
+            continue
+        matches.append(attrs)
+    return matches
+
+
+def main():
+    # Simulate a character tag with many image variants.
+    # Visual novel characters can have dozens of emotion/pose/outfit combos.
+    num_images = 200
+    attrs_per_image = 8
+    num_required = 30
+    num_optional = 30
+
+    # Build a pool of attribute names
+    all_attrs = [f"attr{i}" for i in range(num_required + num_optional + attrs_per_image)]
+
+    required_list = all_attrs[:num_required]
+    optional_list = all_attrs[num_required:num_required + num_optional]
+
+    required_set = set(required_list)
+    optional_set = set(optional_list)
+
+    # Build image attribute tuples. Each image has some required, some optional,
+    # and some unique attrs.
+    image_attrs_by_tag = []
+    for img_idx in range(num_images):
+        attrs = tuple(
+            required_list[img_idx % num_required:img_idx % num_required + 3]
+            + optional_list[img_idx % num_optional:img_idx % num_optional + 3]
+            + [f"unique{img_idx}_{j}" for j in range(attrs_per_image - 6)]
+        )
+        image_attrs_by_tag.append(attrs)
+
+    # Correctness check
+    result_defective = simulate_defective(image_attrs_by_tag, required_list, optional_list)
+    result_fixed = simulate_fixed(image_attrs_by_tag, required_set, optional_set)
+    assert result_defective == result_fixed, (
+        f"Results differ: defective={len(result_defective)} fixed={len(result_fixed)}"
+    )
+    print(f"PASS correctness: both return {len(result_defective)} matches")
+
+    # Benchmark
+    iterations = 2000
+
+    start = time.perf_counter()
+    for _ in range(iterations):
+        simulate_defective(image_attrs_by_tag, required_list, optional_list)
+    defective_time = time.perf_counter() - start
+
+    start = time.perf_counter()
+    for _ in range(iterations):
+        simulate_fixed(image_attrs_by_tag, required_set, optional_set)
+    fixed_time = time.perf_counter() - start
+
+    ratio = defective_time / fixed_time if fixed_time > 0 else float("inf")
+    print(f"PASS benchmark: defective={defective_time:.3f}s fixed={fixed_time:.3f}s ratio={ratio:.1f}x")
+    assert ratio > 2.0, f"Expected at least 2x improvement, got {ratio:.1f}x"
+    print(f"PASS ratio > 2x confirmed ({ratio:.1f}x)")
+
+
+if __name__ == "__main__":
+    main()