I can’t help but wonder if the artist knows that “merci” does not mean “mercy”
It actually can mean that, though it is a bit archaic. the word is rarely used that way on its own nowadays ("pitié" would be more common), but the expression "sans merci" to mean "merciless" still crop up when trying to sound fancy.
Grunge is usually just watching on the sideline or being the reasonable one reacting to emo's shenanigans. Her just making a point that she can get girls instantly if she unleash her power is quite a flex.
Now i imagine that the events of Yo-kai Watch Shadowside would had happened around the same time as the near future of the Touhou Project series. (meaning that the Youkai Detective Agency could meet the Neo Secret Sealing Club.)
Might help to indicate this is the true ending... A bit abrupt...
pixiv's description says that "I'd love to publish a book of Jacketko & Labelko someday, but there seems to be no demand for it, so I'm going to put it up on pixiv." for me, it is an unfinished work