Convert your input to int
and drop all those lists:
print('Welcome to the game')
char1=input('What is the fist characters name: ')
char2=input('What is the second characters name: ')
char1st=int(input('What is the strength of '+char1))
char1sk=int(input('What is the skill of '+char1))
char2st=int(input('What is the strength of '+char2))
char2sk=int(input('What is the skill of '+char2))
strmod = abs (char2st - char1st) / 5 # or // 5 for floor division
#and so on