The following guns are seen the anime Mezzo: Danger Service Agency.
Mikura Suzuki uses a M1911 as her weapon of choice. Asami uses this weapon briefly in Episode 8 to save Mikura from the virtual Black Scissors gang.
The Beretta 92FS is used by the Black Scissors enforcers. Most notably in the opening of the first episode, where every member of the Black Scissors draws a Beretta 92F and opens fire at Mikura.
The Beretta makes another appearance during Episode 10. In the hands of one of the hijackers.
In Episode 1, Mikura carries a Franchi SPAS-12 shotgun when the DSA team goes after Asano. She first uses the gun to blast the locks off the door to Asano's apartment. Then later against Asano himself, using the weapon to suppress and destroy his cover. Sadly, her SPAS-12 is never seen again.
After being pinned down by Mikura's shotgun fire, Asano retaliates with an M16A1 fitted with a M203 grenade launcher. He never fires the rifle itself, instead launching a 40mm grenade at Mikura and company.
M203 Grenade Launcher
Asano fires the M203 from his M16 to escape from Mikura and company.
Heckler & Koch MP5K
In Episode 3, a former client attacks Mikura and Harada with a Heckler & Koch MP5K fitted with a 15-round magazine. Mikura manages to disarm the former client and takes his MP5K for herself.
The MP5K appears again in Episode 10, in the hands of some of the hijackers.
Heckler & Koch MP5A2
The assassin, Kazuto, attacks Kurokawa with a MP5A2 twice in Episode 12.
Mikura carries this gun when she tries to infiltrate a gang's hideout in episode 7. She draws it when her cover is blown, but quickly finds herself outgunned when the leader of the gangsters grabs a sub-machine gun. (Can someone help me identify this, please? I honestly have no idea what this gun is.) [answer: double barrel derringer]
"First Model" CZ 75
Kurokawa (Pops) uses a "First Model" CZ 75 throughout the series.
The gangster boss in Episode 7, uses a Steyr TMP when Mikura's cover is blown. Another Steyr TMP is seen with a silencer when the gangsters chase Mikura into the alley.
Some of the hijackers in Episode 10 are also using Steyr TMPs.
In Episode 11, there's a (very) brief glimpse of a Mauser C96. Mugiyama attempts to draw this gun after he and Kazuto have a little "disagreement".
Some of the bodyguards in Episode 11 are carrying MAC-10s with foregrips.
In Episode 9, Mikura apprehends a thug who draws what appears to be a Walther P38.
Asona draws a Walther P22 near the end of Episode 1.
Kazuto uses what appears to be a H&K PSG1 at the end of Episode 1 and the beginning of Episode 2. He attempts to assassinate Kurokawa with it, but is thwarted by Mikura. He makes another attempt in Episode 3, but backs out when he's spotted by Asami.
Smith & Wesson Model 36
Kazuto briefly uses what appears to be a Smith & Wesson Model 36 in Episode 12.
One of the crooked cops in Episode 12 carries a Desert Eagle.
AMT Automag III
The crooked cop in Episode 13 uses what appears to be an AMT Automag III.