Can I move diagonally across the corner of enemy spaces without tumbling through?

Question

Imagine that on each edge of your square stands an enemy, but the diagonals are not occupied (□: unoccupied square, E: enemy, P: player):

□ E □
E P E
□ E □

Do you need to Tumble Through? Based on its text, tumbling is only necessary if you want to be (temporarily) in a square:

[...] During this movement, you can try to move through the space of one enemy.

Is diagonal movement unhindered?

Answer 1

It is unclear, but likely yes

Moving through a creature’s space seems to be mostly about how you can avoid ending up in with 2 creatures in one square:

If you want to move through an unwilling creature’s space, you can Tumble Through that creature’s space using Acrobatics. You can’t end your turn in a square occupied by another creature

When you move diagonally, there is no chance that you finish in their square, so Tumble Through seems unnecessary.

Answer 2

The rules don't say

The closest rules presented in Movement in Encounters and Running Encounters include things like:

• Diagonal movement cost
• Moving through a creatures space (no reference to adjacent enemies)
• Objects can restrict movement (no reference to how corners affect this)

Each GM will have to make their own determination of how to rule this based on a couple core questions. The crux is deciding if diagonal movement (from one 5-foot area to another) constitutes moving 'through' one or both of the 5-foot squares orthogonal to them. (This could also have implications regarding diagonal movement around an enemy, but that's another ruling entirely.)

• Allowing the diagonal movement is closest to RAW because there is no specific dis-allowance for moving between enemies, nor any specific reference to moving through any spaces not included in your Movement
• Dis-allowing the diagonal movement is a potentially more immersive ruling... it doesn't take 8 people to surround someone, it doesn't require special ruling to prevent you from moving through the corner of objects that are pushed together, it makes it possible to block passages that happen to be on a diagonal portion of the map, etc.