Go for an imp.

You're a Demonologist. It only makes sense to select a demon rather than an elemental. And having a critter, while possibly serving as a useful utility, ultimately sounds lame. Besides, maybe you can conjure up some of those as necessary with your other summoning spell. In other words, there's really only one choice. You select Imp, and the menu vanishes.

Then the spell actually begins. It feels pretty normal, just standing in place and making magical motions. But there's a new component to it as well, you realize. The text in the tome begins to glow yellow. Not all of it, only one or two sentences. You're pretty sure you're supposed to recite them, and due to your class upgrade you can now understand what it says, so fortunately you won't have to spend a few years learning a new language.

You read the sentences out loud, the words you speak sounding about as generically evil as you anticipated. At times it sounds like you're talking backwards, and even though you're the one doing it you're not sure how it works. As you finish the marked text, another piece lights up. You continue to read, like some weird karaoke, while a glowing red pentagram begins to form at your feet.

This is kept up for several minutes. You start to worry that Morwyn will get bored, but glancing over at her she still seems engaged. You just try to maintain concentration, fearing the embarrassment of having to start over. The pentagram before you is slowly spinning now, its edges lined with demonic signs. Then, suddenly, it seems to... open up.

The star inside the circle appears to slice open space itself, forming a swirling, fiery portal. You continue reading from your book and waving your fingers evilly, and then the portal spits out a jet of fire before abruptly closing up with what sounds like an explosion played in reverse.

You finish the ritual and the fire left behind dissipates, revealing a small figure that was concealed within. It drifts down to the ground and looks around, disoriented.

Yup, that's an imp alright. Red skin, glowing yellow eyes, tiny little horns, a pair of batlike wings and a tail ending in a sharp spike. It is also clearly female, on account of its surprisingly curvy physique and perky C-cup breasts. Or well, they would be C-cup if the imp was human-sized. But instead, she's even shorter than you, standing only two feet tall. She is pretty cute though, with her wide face and somewhat exaggerated facial features. Also breasts. This is the first time you ever see an unclothed pair, and it's filling you with urges your body was not designed to satisfy.

She finally comes to her senses as her eyes settle on you. She then bends her knees in what you think is a curtsy.

"Greetingsh, my new mashter!"

Great. You got one with a lisp. Oh well, maybe you'll look less silly and cute next to her. Also, master? Fuck, did that feel good. You have a minion now. And she addressed you as "master". You have only fantasized about that until now...

Morwyn excitedly claps her hands at your display. "She's adorable! We basically have a little monster-possy now!"

The imp turns around, suddenly made aware of Morwyn's presence, and she takes a battle stance and begins to conjure fire in her palms. Right, she's still a monster and your companion is not.

"No!" you order her. "She's a friend. Leave her be."

Confused, the imp flicks her wrists and makes the fire dissipate, turning back to you. "...Really?"

You nod, relieved that you do indeed control her.

Morwyn stands up from her rock. "Yeah, we're on the same team apparently. I don't really get it either, you just have a weird master." She then crouches in front of her and extends her hand. "I'm Morwyn, who are you?"

The imp looks to you and you nod in approval, to which she extends her hand as well for a handshake with a very notable size difference.

"I'm an imp," she says.

Morwyn rolls her eyes as she lets her hand go. "I knew that, I meant your name. Do monsters just have no names?"

"I'm not important enough to have a name," the imp replies. "That ish resherved for greater demonsh. Or hero familiarsh."

"Well you're the familiar of a hero familiar, or however that works, so I think you deserve a name." Morwyn looks over to you. "Wanna name her?"