He uses his latent energy to transcend his limits, but the book does not say he hits with planet destroying force in that form.
Here's the scan with the raws
- 星を消し飛ばすほどの威力を誇るボロスの究極技「崩星咆哮砲」に対抗するべく、サイタマが繰り出したのは「マジ殴り」。これまで普通のパンチ一撃で決着をつけてきたサイタマだが、壮バトルについに切り札を出す!!
Now here's everything besides the hoshi translated
- In order to oppose Boros' ultimate technique the [Collapsing Star Roaring Canon] which boasts enough power to blow away a [星], what Saitama pulled out was a [Serious Punch]. Even though up until now every battle had been concluded with a normal punch, he finally uses his trump card to end a terrific battle!!
Now can you tell me context wise, why it should be read as 'Star' rather than 'Planet'? Every other usage of hoshi in the series refers to just the planet Earth, including the anime this book is based on and including this book one page ago. There's no evidence that it should be read as 'Star' rather than 'Planet'