Ren as the main attacker, Mei as active back-up

There was a large number of them, and there was no way Ren could handle them all on his own.
No matter how much of a cannon fodder they were, he still wasn't strong enough to deal with 20 of them by himself.

Therefore they decided to fight together, even if it'd mean Mei would have to exhert some of her energy... maybe it wasn't wise to **** her damaged cultivation just to deal with some small fries, but better to be safe than to be sorry.

It sounded like a plan, and they acted on it.

Ren activated his Human Eye and began to snipe them in order to thin their numbers while attracting them over.
He managed to kill off 4 of them, and once the Jakis were upon them he slashed with his sword beheading yet another one!
But for each he killed, two more would take their place and if not for Mei attracting most of them, he'd soon be overwhelmed by their sheer numbers.

As for Mei... she was indeed being ganged upon by at least ten of them, but her power was leagues beyond Ren and since she wasn't holding back she could easily deal with the Jaki and their miasma.
Those vermins were obviously aroused and their number wasn't little so theoretically her body should be starting to feel some heat, but with her actively using her energy she could easily fend off such tricks and continue beating the living daylights out of them!

It took some time and there were some dangerous moments for Ren, but eventually all the ambushing demons were dealt with and the couple managed to scavenge 18 coins worth of demon cores, a great gain though this could only be considered a shallow victory due to how much energy Mei had to waste during the fight.

[Mei Qi decreased by 20]