Stuck to the Wall

If Nathan knew what Bella was thinking he would probably be speechless.

The reason for cutting the Null fruit like that was because he doesn't want her to literally explode.

Since the Null Fruit he gave is an intermediate grade one, the energy contained in that one fruit probably has the potential to make a normal human explode if they ate it.

It was something that Nathan realized when he ate the Null Fruit before as well.

The reason that he felt full after just eating 7 Null Fruit was because the energy it had was filling up his whole body and not just 'mindlessly' raising his level.

Meaning, there's a possibility that if someone consumes too much in a short span of time, their body won't be able to handle it hence exploding.

For Bella's safety, he only gave her ¼ of the intermediate Null fruit as it contains more than 10 times the energy within a low grade Null Fruit.

He's not even sure if that amount of Null fruit is alright for a normal person such as her to eat.