How to indicate a single required field in a big form?

Question

Foreword: this form is a UX nightmare in itself. My task is not to make it better, just to show a required field.

I have a form in which the user can add multiple lines to a dynamically added group of data called "activities". These lines ultimately become the budget for said activity.

Each of these lines come with a field called "justification". This field is required to be entered by the user, or else he won't be able to save his work.

Here is what it looks like:

The highlighted column is the required field. As previously stated, this is the only field in the whole form that will prevent the user from saving.

So, how do I indicate to my user that this field is required in a sea of other fields that are not?

Answer 1

As you would not like to improve usability at a high level, the best solution could be prevented to reinvent the wheel. Use the most common required field icon: * aside from the justification.

This simple action will prevent to make your user think. Will be natural and easy to understand.

As advanced you also can highlight the input with a red line around. But this could look like and error without submit the form.

And to prevent errors, when submit verify the fields and show an error message if some information is missing.

BUT, if you need something more advanced to improve the usability you can bring some alternatives that you think and we can discuss.