Everyone's advice here is really good; introduce some kind of problem that affects a sympathetic character directly.
So for my comic, I introduced three characters: Rekki, a wannabe magical knight who is bad magic (relateable, sympathetic main character), her BFF Sarin, who is also a wannabe magic knight but actually good at magic and is a very conscientious, kind person who maaaaybe has a little crush on Rekki (it was important to set up Sarin as basically being a really great person for later) and Urien, their mentor, a rather unpleasant narcissistic guy who tries to play them against each other to get what he wants.
I set up a mysterious ruin they're in that they're not meant to be, so the general vibe is suspense, but I also threw in some comedic moments to establish "this comic has a comedic tone" and to make people like Rekki and Sarin more (being funny makes a character likeable), and then I threw in a surprise curveball that creates suspense. The legendary sword Excalibur is in the ruin!
So in checklist form (and yeah, I legitimately did write a checklist):
- The opening will contrast the way the comic ultimately ends in an interesting way.
- The opening establishes the important conflict of the story.
- The opening establishes a point of view character and makes them either likeable or compelling.
- The opening should set the tone of the story and what sort of content to expect from it.
I generally try to keep dialogue to the same amount as in any other page of my comic. Ideally one sentence per speech bubble or two at a push, and no more than one or two speech bubbles per panel if I can help it. The text needing to be big for mobile readers honestly makes it pretty hard to break these rules! 
So if you do decide to do an "opening narration crawl", break up the text and use plenty of compelling pictures. The opening of Magical Boy did it well:
https://tapas.io/episode/1051887
Lots of beautiful pictures, not too much text and then it quickly leads us into the characters, the tone and the immediately relevent conflict. This comic has to establish the lore first because we have to know that magical girls are a thing in this world so we can have the subversion: The person who has inherited the "magical girl" powers is a trans man.
As a general rule, only do a narration crawl if it is genuinely the best way to establish vital information your story cannot function without the audience knowing. Like Avatar the Last Airbender, the audience needs to know about the 4 nations, that the fire nation attacked and that there's a special magical person called the Avatar.
Do not make an opening text narration with abstract pictures, stock images or just text floating on a blank or textured background and just some vague stuff about "long ago... there were legends... but the legends.... went away.... but now... a new legend.... is beginning...?" as an excuse to put off having to actually draw characters or scenery or commit to planning out a story! (I see this so much in new creators. I definitely did it myself when I was a teenager!
)