Reference to an Aesop fable. In the original version, the scorpion stings the frog and both of them drown. The moral is that some people are intrinsically harmful, even against their own self interest
There's an old fable about the frog and the scorpion.
Paraphrasing, the scorpion asked the frog to be carried over the river, because otherwise he'd drown. The frog was reluctant, saying "but you'll sting me".
To which, the scorpion says, "but then I'd drown! so I won't do that".
Persuaded, the frog agrees. As they were crossing the scorpion stings the frog, and the frog asks, "Why would you do that? now we both die!"
and the scorpion replied, "because it's in my nature"
"o7" is a saluting text emoji. The 'o' represents a head, and the '7' is a raised arm. It's usually used in internet culture when a fictional character dies, or when one dies in a video game.
Similarly, there's the "Press F to pay respects" meme, which appeared as a quick time event in a video game cut scene (Call of Duty, I think?), and was adopted into sarcastic use by the internet, so "F" and "o7" are kinda used interchangeably.
Well, I don't think those are interchangeable. o7 is used like "I salute you" or like "roger that", while "F" to pay respects is more like "my condolences".
And to be a tad pedantic, it's an "emoticon" or "emote", not an "emoji".
Text emoji is kaomoji, which is the Eastern branch of emoticons, so you're right, technically it wouldn't generally include o7, but that's kinda splitting hairs.
You're also right, o7 has more broad uses than F, but they do both get used in a usually tongue-in-cheek "condolences" manner. So you can almost always use o7 in the place of F, but not necessarily the other way around.