Harlequin as an SA Survivor
This is more speculation on my part than based on concrete evidence, but I've tossed this possibility around privately before and might as well share publically.
For me, TFC has a lotta themes around sexual violence, bodily autonomy, and power & control, especially towards women. This is most prevalent with the story of Columbina and the situation with Carol ( @purple-plum-petals did a good break down about this topic here) but I feel like it pops up in the few things we've learned about Harlequin both in-game and from @nekoboydreams posts.
These're already heavy subjects media is cautious to tackle but especially when it comes to male victims. The fact Harlequin (and the rest of the troupe) are foreigners on top of having a 'disability' as monsters trying to masquerade as 'normal' humans --both who are more likely to slip through the cracks in society when it comes to assistance-- feels reflective of the Fools especially with Carol as the current 'face' of the Fools (I refuse to believe that the darkest-skinned character being kidnapped and our way to empathize with the Fools' predicament wasn't a coincidence). If Neko made one of the two male leads also a survivor it'd be huge to see.
Harlequin is the youngest of the troupe, is charming and quick-witted, is the second-smallest as well. In the present he's the most physically intimate but balks at emotional vulnerability unless it's through a sexual lens. Him having faster reflexes than Pierrot but never fighting back or running when the latter harms him, possibly because that's the only kind of touch Harlequin feels 'allowed' to. His rejection of love and focusing instead on hatred as a basis for a relationship?
Dunno, just some food for thought. Would love to hear others opinions
Also thank you @tentsentslime for the reminder about Arlo's age!