When you look at different League of Legends champions, some of them tout weapons in their splash art that they actually use. Leona uses her sword and shield, Miss Fortune uses her gun, Gangplank uses his pistol, and the list could go on and on.
Malzahar is a tricky case. You may have noticed that he carries around a dagger but never uses it. According to Riot Tiger Lily, an Editor as well as part of the Worldbuilding Team, Malzahar carries the dagger because of a very troublesome story that happened in his life.
"Little known completely non-canonical fact: Before staring into the Void, Malzahar used his seer abilities to wow Shuriman crowds as he toured with a traveling fair from town to town. In each new city, he’d ask for a brave volunteer from the audience to stand against a circular wooden target, affixing their wrists and ankles against it with snug straps. Hoisting the target into a spin, he’d turn and walk eighteen paces away from it, tying a blindfold around his eyes. Like lightning striking without warning on a cloudless day, he’d spin on his heels on his eighteenth step and fling five daggers at the target, each landing within a hair’s split from his volunteer’s body. Though he was a born seer and his ability to look into the future made it easy to know where the target was at any given moment, he breathed a sigh of relief as he counted the thwip, thwip, thwip, thwip, thwip of the daggers digging into the wood."
"On a particularly lovely spring evening in Urzeris, Malzahar looked over the fluttering hands of the crowd, waving like kelp in the sea trying to get his attention, and chose a beautiful raven-haired woman with eyes like emeralds. He slid the straps around her delicate wrists, spun the target, and began to count… fifteen…sixteen…seventeen…eighteen…"
"…thwip, thwip, thwip, thwip – thunk."
"Malzahar keeps the dagger that ended her life with him always, to remind himself that even a seer can’t predict the uncertainty of the future. There is always a chance things can change – for better, and surely for worse."
Well, that's certainly an interesting story that definitely allows Malz to carry around his dagger. I'm not going to argue with the story and neither should you.