diff --git a/src/llvm_py/instructions/boxcall.py b/src/llvm_py/instructions/boxcall.py
index 462590de..ec985ea1 100644
--- a/src/llvm_py/instructions/boxcall.py
+++ b/src/llvm_py/instructions/boxcall.py
@@ -103,8 +103,8 @@ def lower_boxcall(
         if recv_val is None:
             recv_val = ir.Constant(i64, 0)
 
-        # Phase 287 P4: Box primitive i64 first, then invoke toString via universal slot #0
-        # SSOT: nyash_box_from_i64 creates IntegerBox handle, then plugin invoke with method_id=0
+        # Phase 287 P4: Box primitive i64 first, then call universal slot #0 SSOT
+        # SSOT: nyash.any.toString_h(handle) -> StringBox handle (works for ALL types)
         if hasattr(recv_val, 'type') and isinstance(recv_val.type, ir.IntType) and recv_val.type.width == 64:
             # Step 1: Box primitive i64 → IntegerBox handle
             box_i64_fn = _declare(module, "nyash.box.from_i64", i64, [i64])
@@ -116,16 +116,12 @@ def lower_boxcall(
             # Already a handle
             recv_h = _ensure_handle(builder, module, recv_val)
 
-        # Step 2: Invoke toString via universal slot #0 using plugin system
-        invoke_fn = _declare(module, "nyash_plugin_invoke3_i64", i64, [i64, i64, i64, i64, i64, i64])
-        type_id = ir.Constant(i64, 0)  # Type resolution deferred to runtime
-        mid = ir.Constant(i64, 0)  # method_id=0 for toString (universal slot)
-        argc = ir.Constant(i64, 0)  # No args for toString
-        a1 = ir.Constant(i64, 0)
-        a2 = ir.Constant(i64, 0)
-        result = builder.call(invoke_fn, [type_id, mid, argc, recv_h, a1, a2], name="slot0_tostring")
+        # Step 2: Call universal slot #0 via nyash.any.toString_h (SSOT - no plugin invoke)
+        # This works for IntegerBox, FloatBox, BoolBox, StringBox, ArrayBox, etc.
+        tostring_fn = _declare(module, "nyash.any.toString_h", i64, [i64])
+        result = builder.call(tostring_fn, [recv_h], name="slot0_tostring")
         if os.environ.get('NYASH_LLVM_TRACE_SLOT') == '1':
-            print(f"[llvm-py/slot] Invoked toString via plugin (method_id=0) on handle", file=sys.stderr)
+            print(f"[llvm-py/slot] Called nyash.any.toString_h (universal slot #0)", file=sys.stderr)
 
         if dst_vid is not None:
             vmap[dst_vid] = result