Plot multiple kind of diagrams within each subplot using Pandas

I would like to make subplots (bar diagram) and draw another line graph within each subplots. Pls, note that I am able to see it is reflected in the legend but I can't see them in the graph. Consider the code below as an example.

import pandas as pd
import random
import matplotlib.pyplot as plt

df = pd.DataFrame({'year': range(2000, 2010)})
df['var1'] = [random.randint(10, 50) for x in range(10)]
df['var2'] = [random.randint(10, 50) for x in range(10)]
df['var3'] = [random.randint(10, 50) for x in range(10)]
df['var4'] = [random.randint(10, 50) for x in range(10)]
df['var5'] = [random.randint(10, 50) for x in range(10)]
df['var6'] = [random.randint(10, 50) for x in range(10)]

keys = df.keys().values                 # Column names

fig = plt.figure(figsize=(10,10), constrained_layout = True)
i = 0 # For subplot positioning only

for count in range(1, len(keys), 2):
    i += 1

    axis = fig.add_subplot(3,1,i)
    graph = df.plot(x='year', y=[keys[count], keys[count+1]], kind='bar', ax=axis, legend=None)

    ## Wanted to plot another line graph within subplots
    line_plot1 = df.plot(x='year', y=keys[2], ax = axis)