Ichigo Kurosaki, the protagonist of the anime/manga series Bleach, uses a strong technique called Getsuga Tenshou. It is highly compressed energy that can be used to strike enemies far away. But the case where Getsuga Tenshou may not work is quite a few.

However, there is one situation when Getsuga Tenshou will not be effective, i.e. when the enemy is too strong. For instance, Aizen effortlessly deflected Getsuga Tenshou when Ichigo used it against Aizen during the Hueco Mundo arc. This was because Ichigo had much less strength than Aizen at the time.

In another circumstance, Getsuga Tenshou will not work if the opponent has some particular ability to nullify it. For instance, Byakuya was able to use his Bankai to block Getsuga Tenshou when Ichigo used it against him in the Soul Society arc.

However, Ichigo might be too weak to use Getsuga Tenshou. For instance, when Ichigo was engaged with Ulquiorra Cifer during his fight at Las Noches Arc, he was so severely wounded that he could not use Getsuga Tenshou effectively.

Other than these situations, there are a couple of things that can hinder the effectiveness of Getsuga Tenshou. This can be shown, for instance, by the amount of spiritual energy Ichigo possesses, which will determine the type of attack and its power. Moreover, the attack can be stopped or diverted to an offensive by physical objects like walls or swords.

In brief, Getsuga Tenshou is definitely powerful, but has its own constraints. The attack may not work in a couple of situations and some things also affect its effectiveness.