I've said this in another thread, so I'll summarize it here. Sony can't buy Square. They don't have the liquidity to do it
Square's market cap (according to Google) is 689 billion yen. In just cash, Sony has 1.473 trillion yen. However, this is split between all of Sony's departments. If you take out Sony Financial Services, they only have 874 billion yen. This means Sony would either have to go into debt or spend all their cash to buy Square. Even if they do a half cash, half stock deal, then it's still costing them 345 billion yen, and would only leave all of Sony's divisions (sans Financial Services) with 529 billion yen. One thing to keep in mind is Sony does not have a lot of liquidity, so to lose this much cash puts them at a pretty big risk. Also, Sony has a lot of short term debt (1.478 trillion which is more than the cash they have on hand) and a decent amount of long term debt. They don't have the money to throw around.
Moreover, if Sony did this, you'd see Nintendo and probably Microsoft throw their hat into the ring to prevent this from happening. Nintendo has 1.07 trillion yen and has far more liquid assets (securities and CDs) than Sony does, so they could throw more money around than Sony could, if a buy out was possibility. Not to mention they have less debt. They also have a lot to lose if Sony bought Square, since Nintendo pushes for Dragon Quest, has smaller developers that make third party content for them (Octopath/Braverly Default) and legacy content (and Smash I guess). So even if Sony could do it, they'd likely get outbid in the end.
By the by, there is a reason why you haven't seen Sony make a lot of big acquisitions, or many acquisitions to begin with.