Shardblade ability?

[Zmaray he/him]

Which of the three realms does a shardblade affect when it strikes living flesh?

[Weltall]

The Spiritual. Here's a collection of WoB's where Brandon talks about how Shardblades damage living matter by directly cutting the soul. Once something is dead, it can be cut by a Shardblade in the Physical Realm as well.

[Yata he/him]

Like Weltall said the Shardblade cuts the Spiritual and the Physical with the Spiritual as primary target.

Probably the difference between living and not targets is all in the amount of Soul's Investiture. A living being's soul is really greater and more Invested so the Blade can't cut both the Soul and the Physical at the same time. For unanimate target the Blade's cut is enough to destroy the soul and also affect the physical