Raditz is the evil brother of Goku, and is a violent Saiyan as opposed to Goku, who never had the tendency to be evil. For this reason, Raditz hates Goku. Your goal is to kill Raditz. This is arguably the hardest battle yet. Every strategy you use has to be a safe one, but that doesn't mean you should back off with those Ki attacks. Weaken him and be patient. You'll get him to 0 HP in no time.
If none of the battles have yet proven challenging to you, then prepare for a challenge. If you're still getting the grips on battle strategies and attacking/defending, then this will be a hard one. It's impossible to have more HP than him, but it is possible to have more Ki than him. Still, staying safe is what's going to win you the battle here. Try to keep your HP as high as possible. The reason why HP in this battle is so essential is because you're in danger once your HP goes below 200. If your HP goes even a little under 100, then Raditz will unleash an attack so devastating, you'll die immediately. Even if his HP is lower than 50, he can use that move at anytime. So try to keep your battle strategies a little safer for this battle, and take your time. Being slow doesn't give you a disadvantage, so no matter how long it takes to get his HP down to 0, just stay safe and use those Ki attacks.
Unlike the previous battles you've faced, you won't start first this time. Instead, you start with defending. Go down to the defense section to start on that, but for now, this is after your first defense. You should now have 5 available moves. After the first turn, you should be somewhere closer to Raditz. This is good for you, since you don't have to move up and then back, but only back. Also, remember that if you're attacks aren't strong enough, they can even backfire on you. Surprisingly, Raditz can attack when you're the one attacking. This can be tiring and seem unfair, but the battles will only get tougher from here. Chain your attacks with strategy, and start with a punch or a kick before going crazy with Ki attacks. You can also try saving your Ki until your HP reduces by 100, but make sure the HP of Raditz is going down as well. If it's not moving, it's likely that your attacks aren't strong enough. In times of desperation, also remember that you have a Kamehameha ready.
You start defending first, since the SP bar of Raditz fills up first. Block or dodge whenever you can, and you won't take as much damage as you would have. Most of the time, try blocking. Dodging isn't as effective, and you'll lose more HP. It's a little harder than dodging, and both depend on reflexes, but you can miss a few blocks. A frequent move of his only takes 30 of your HP. Since you should have over 800 HP by this point, it's okay to take a few misses, and dodge when you feel you've missed too many blocks. Just stay safe.