: This is a unique "canary" string. By concatenating these specific characters, the attacker is looking for this exact text to appear on the webpage. If it shows up, they know the injection was successful and which column can be used to extract data.
: The series of NULL values is a "column matching" tactic. The attacker is trying to figure out exactly how many columns the original database table has so the UNION command doesn't crash the system. : This is a unique "canary" string
This sequence isn't a narrative in the traditional sense, but rather a set of instructions for a server: : This is a unique "canary" string