This has got to be the cockiest fucking MC I've ever read.
Usually the "I got forced into martial arts when I was a kid" background is only there to justify the MC having a head start in being good at fighting and never gets acknowledged beyond that but this dude is actually so fucking cocksure of his own sword skills at all times.
Oh yeah let me pick a fight with these glowie adventurers from America because I'm sure I can stab them in the gut before they can pull their gun on me. Oh yeah let me pick a fight with this top Japanese adventurer because her sword skill is 1 rank lower than mine so she's weaker than me. Oh yeah let me pick a fight with the royalty from another world with unknown powers because I'm sure I can chop off their heads faster than they can do anything.
The power levels in this work are really low for gateshit too, so being "really fucking good" with a sword is just that, not like the MC can flash step or fire sword beams or dodge bullets or anything.