Dark Knight Simple yet effective buff idea

[Carighan]

Please, can you remind me what is the job of a tank?

In FFXIV's raids? The job is dealing damage. The same as healers and damage dealers do as their primary function.

A secondary function, given by role and fight design, is that players playing tanks will automatically hold the bosses' attention at no further input needed, and will sometimes be prompted (usually by a specific marker, but there are a few of them) to press usually a combination of two buttons, with the one with the bigger CD sometimes alternating. There are also moments they press a single button instead, but they're also prompted by markers or specific cast bars and designed into each particular fight.

As far as actual gameplay goes, nope, the job is dealing damage and that's it. Again, same as the GCD-part of playing a healer. :P