Genos is an extremely serious character. He constantly strives to become stronger and pesters Saitama to train him frequently. Since becoming Saitama's disciple, Genos is very reverent and protective towards his "teacher", although he does express annoyance and disbelief at the mundane training regimen Saitama used to gain his powers.
On most occasions, Genos acts as a comic foil to Saitama's clueless antics, using a variety of special techniques, battle tactics and robotic upgrades to combat villains (and sustaining terrible damage in the process), only to be outclassed by Saitama with a single punch. Due to Saitama's incredible strength, Genos is led to believe that there is a secret to Saitama's power.
Despite their disparity in strength, Genos' diligence earns him greater recognition than his mentor. His superior acumen granted him immediate status as an S-Class Superhero within the Hero Association, compared to Saitama's C-Class designation. He also possesses seemingly vast wealth, enough to repair or upgrade his cyborg body and cover Saitama's rent on a regular basis.
He eventually mellows out, and he recognizes that this is due to Saitama's influence. He eventually comes to respect Saitama not just for his power, but also for his character. This was shown when Genos remarks on how similar Handsomely Masked Sweet Mask is to Genos's former self when Sweet Mask brutally dispatches a group of alien prisoners with no mercy.
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