be up to vs become

be up to

verb
  • To depend on, to be the choice of. 

  • To do or be involved in doing; to do (often something mischievous or inappropriate). 

become

verb
  • To be proper for; to beseem. 

  • Of an adornment, piece of clothing etc.: to look attractive on (someone). 

  • To come about; happen; come into being; arise. 

  • begin to be; turn into. 

How often have the words be up to and become occurred in a corpus of books? (source: Google Ngram Viewer )