diff --git a/main.py b/main.py
index e1fe8cd..0276c28 100644
--- a/main.py
+++ b/main.py
@@ -3,7 +3,7 @@
 import matplotlib.pyplot as plt
 import pandas as pd
 from matplotlib.patches import FancyArrowPatch
-from matplotlib.widgets import Slider
+from matplotlib.widgets import Button, Slider
 from mpl_toolkits.mplot3d import proj3d
 
 connection = [
@@ -28,11 +28,17 @@
 
 # Configure vectors to draw (list of (start_index, end_index) using 0-based indices)
 # Edit this list to add/remove vectors to display
-VECTOR_PAIRS = [(4, 5), (12, 13)]
+VECTOR_PAIRS = [(4, 5), (9, 8)]
 # Optional colors (will cycle if fewer colors than VECTOR_PAIRS)
-VECTOR_COLORS = ["r", "b"]
+VECTOR_COLORS = ["r", "g"]
 # Line width for vector arrows
 VECTOR_LW = 4
+# Optional labels for vectors (defaults to v1, v2, ... if None)
+VECTOR_LABELS = None
+# Label offset factors: fraction of vector (x/y) and fraction of z-range to offset label position
+# Increase these to place labels further from the vector
+LABEL_OFFSET_XY = 0.12
+LABEL_OFFSET_Z_FACTOR = 0.05
 
 
 # 3D arrow helper to draw arrows between 3D points
@@ -44,6 +50,9 @@
     def draw(self, renderer):
         xs3d, ys3d, zs3d = self._verts3d
         xs, ys, _ = proj3d.proj_transform(xs3d, ys3d, zs3d, self.axes.get_proj())
+        # If projected endpoints are effectively identical, skip drawing to avoid path errors
+        if abs(xs[0] - xs[1]) < 1e-6 and abs(ys[0] - ys[1]) < 1e-6:
+            return
         self.set_positions((xs[0], ys[0]), (xs[1], ys[1]))
         super().draw(renderer)
 
@@ -158,6 +167,32 @@
         ax.add_artist(a)
         arrows.append(a)
 
+    # Create labels for each configured vector (v1, v2, ... by default)
+    arrow_labels = []
+    labels = (
+        VECTOR_LABELS
+        if VECTOR_LABELS is not None
+        else [f"v{i + 1}" for i in range(len(VECTOR_PAIRS))]
+    )
+    z_range = z_max - z_min if z_max > z_min else 1.0
+    for i_pair, (idx1, idx2) in enumerate(VECTOR_PAIRS):
+        x1, y1, z1 = points[idx1]
+        x2, y2, z2 = points[idx2]
+        mid_x = 0.5 * (x1 + x2) + LABEL_OFFSET_XY * (x2 - x1)
+        mid_y = 0.5 * (y1 + y2) + LABEL_OFFSET_XY * (y2 - y1)
+        mid_z = 0.5 * (z1 + z2) + LABEL_OFFSET_Z_FACTOR * z_range
+        label = labels[i_pair]
+        lbl = ax.text(
+            mid_x,
+            mid_y,
+            mid_z,
+            label,
+            color=VECTOR_COLORS[i_pair % len(VECTOR_COLORS)] if VECTOR_COLORS else "k",
+            fontsize=10,
+            weight="bold",
+        )
+        arrow_labels.append(lbl)
+
     ax.set_xlabel("X")
     ax.set_ylabel("Y")
     ax.set_zlabel("Z")
@@ -199,11 +234,30 @@
                 [points[idx1][2], points[idx2][2]],
             )
 
+        # Update arrow labels positions
+        for i_pair, (idx1, idx2) in enumerate(VECTOR_PAIRS):
+            x1, y1, z1 = points[idx1]
+            x2, y2, z2 = points[idx2]
+            mid_x = 0.5 * (x1 + x2) + LABEL_OFFSET_XY * (x2 - x1)
+            mid_y = 0.5 * (y1 + y2) + LABEL_OFFSET_XY * (y2 - y1)
+            mid_z = 0.5 * (z1 + z2) + LABEL_OFFSET_Z_FACTOR * (z_max - z_min)
+            arrow_labels[i_pair].set_position((mid_x, mid_y, mid_z))
+
         ax.set_title(f"Frame {data[frame_idx].frame_number}")
         fig.canvas.draw_idle()
 
     slider.on_changed(update)
 
+    # Button: switch to top-down (Z軸方向＝真上) の視点に切り替える
+    ax_button = plt.axes([0.02, 0.02, 0.1, 0.04])
+    btn_top = Button(ax_button, "X-Y plane")
+
+    def set_top_view(event):
+        ax.view_init(elev=90, azim=0)
+        fig.canvas.draw_idle()
+
+    btn_top.on_clicked(set_top_view)
+
     plt.show()