Ultra Despair Girls (UP)

The max level for Komaru is 99. From one playthrough, I reached level 76. I didn’t notice an increase of XP to level up, so I believe that the XP to level up is consistent, meaning that you won’t be in for much of a grind at the end. You get XP for defeating Monokumas, so defeat as many as possible. There are three skills which aid in XP gain, these are One Nighter (Chapter 1), Daily Effort (Chapter 3) and Ultra Study Technique (Chapter 4). Make sure to keep these on to maximize XP gained. You’ll likely get this before you finish getting the coins for all Truth Bullets. If this and the 1000 KOs is all you have left and you want to grind instead, you can do it when you need to destroy a wall in Chapter 5. If you don't destroy both walls, a bomber will constantly respawn, so you can keep killing it for xp. Ammo will also drop when you are empty. Thanks to LD2013 for the tip. I did it at the start of Chapter 4 as mentioned before.