अनुबाद - जापानी-अंग्रेजी - 彼は堅気であるが、（ギャング）組織のボスに対してアドバイスをする参謀的な役も引き受けている。そのこ...

堅気―KATAGI---The person who left a life of gang.

組織のボス-Soshiki no Boss ---New leader of organazation.(In this context)

～にアドバイスをする――give advice to~~~

~~的な役割をする――do his part as~~~

参謀(SANBOU)―This is the most important word for me because i would like to know its translation in English.In japanese,SANBOU doesn't only imply "Staff" in military term,but also [b]the person who give advice to Boss [/b]in human relationship.
How does it say in English?

"Sanbou" would literally be translated
Strategic Advisor
but in the case of a gang, I think a good nickname for this person might be
The Planner
(or, more manga-esquely,
The Visionary
The Seer
The Angel
or something like that...)