When Mike used Observe, the following window would appear, giving Mike some basic data on their opponent, a window displaying that his Observe Skill went up in Level by one after he had used it just then also appearing. 

[hider=Observe Data]
Name: Taichi Akihiko

Gender: Male

Age: 29

Level: 31

Class: Blank Mage

STR: 20
VIT: 25
DEX: 24
INT: 40
WIS: 25
LUK: 10

HP: 1,500 
MP: 3,000

Resilience: 25
Concentration: 50

A notorious hunter, Taichi is a Blank Mage, a person who uses a very rare and unique form of magic that can take on many different forms. [/hider]

For some reason, unlike perhaps other people Mike has used Observe on with the same leveled Observe Skill, not a whole lot of information was given other than a basic view of his stats and a glance at what his magic could be. Perhaps it was because he was a bit more powerful, but there was also Sayo, who had been immune to Observe before and she was only Level 5. Also he was probably on the same level of strength as the Enforcers they came with. So perhaps the Observe Skill had its limits after all at certain levels. 

So erring on the side of caution, Mike decided to put his guard up and simply wait and see what their opponent would do next.