How to beat Doctor Peace
While the previous boss battle took place in a fairly confined arena, this one is wide open. You will face Doctor Peace in a large open baseball field. This might seem like a bonus as it gives you more leeway and find hiding places to reload your sword, but the Doc has other plans. Doctor Peace mostly relies on his weapons to deal his damage (what happened to "do no harm," eh?), So the open area gets you in a bit of a bind.
Fortunately, you can shield yourself and block most of its shots, but this will drain the sword quickly and you'll spend a lot of time reloading, probably while taking some damage. Instead, you'll want to dodge as you head towards Doctor Peace, flicking the correct analog stick in any direction to get yourself out of harm's way. Anytime you see him take a hit, make sure to dodge or block so he doesn't take up much health and cause you to fly backwards. Get in close and start dealing damage, but be prepared to flee at any time.
Occasionally, Doctor Peace will pause his own attacks and start charging, as indicated by a glowing aura around him. He's invincible in this state, so back off a bit. This attack deals a ton of damage and sends you flying, so make sure you're far enough before it hits. This is also the perfect time to recharge your sword batteries.
It's a long fight and it's more about attrition than combos or crazy maneuvers. Continue to dodge his attacks as you work towards him. Deal damage, then back up and take time to reload if necessary. Repeat this a few times and that's how beating Doctor Peace in No More Heroes on Nintendo Switch.