Simply put, I messed up installing Archlinux and my system didn't have internet so I couldn't do anything. This is the way I solved it.

For once in a long time, I had some trouble setting up WiFi and Ethernet in my Archlinux installation. After finishing and rebooting to the actual system, I couldn't get up dhcp, and neither wifi-menu (netctl) nor network-manager were installed so I didn't have any means to connect to the web and install needed packages. What a vicious circle.

What I had to do was quite simple really: grab again the bootable USB that I used to install the system in the first place, boot it into the installer and then mount my partitions. These are the partitions I created in the installation process, in my case root and home:

mount /dev/sda1 /mnt
mount /dev/sda2 /mnt/home
Then, chroot into it:
arch-chroot /mnt
Now, you're inside your system as root. In my case, I used iwctl to connect to my WiFi (I used to use wifi-menu, I swear it came in the iso, but it didn't this time). Run "ip a" and get the name of your wireless interface, and connect to your wifi:
station wlp01 scan
station wlp01 get-networks
station wlp01 connect YOUR_WIFI_SSID
And you'll be prompted to enter the password. After that I rebooted into my actual system, and I was already able to download packages, so I just downloaded networkmanager from pacman. And that's all, having an internet connection I could install everything I needed:
                  .o+`                 jorge@jorge
                 `ooo/                 OS: Arch Linux 
                `+oooo:                Kernel: x86_64 Linux 5.7.7-arch1-1
               `+oooooo:               Uptime: 55m
               -+oooooo+:              Packages: 663
             `/:-:++oooo+:             Shell: zsh 5.8
            `/++++/+++++++:            Resolution: 1920x1080
           `/++++++++++++++:           DE: KDE 5.71.0 / Plasma 5.19.2
          `/+++ooooooooooooo/`         WM: KWin
         ./ooosssso++osssssso+`        GTK Theme: Breeze [GTK2/3]
        .oossssso-````/ossssss+`       Icon Theme: breeze
       -osssssso.      :ssssssso.      Disk: 6.0G / 190G (4%)
      :osssssss/        osssso+++.     CPU: Intel Core i5-4210H @ 4x 3.5GHz [55.0°C]
     /ossssssss/        +ssssooo/-     RAM: 2247MiB / 3853MiB
   `/ossssso+/:-        -:/+osssso+-   
  `+sso+:-`                 `.-/+oso: 
 `++:.                           `-/+/
 .`                                 `/