This will be so long and rambly. ˋ( ° ▽、° )

Domesticity for ReiMob probably. Guilty Reigen tropes too obviously, but nothing gives me life like fanworks that just look like they could belong in canon, with Reigen & Mob just ~being somewhere~ & ~doing something~ that's probably either spirit or food related. Oh yeah I can also never get enough of food emphasis in mp100.
RM feeding each other... RM being close in casual ways... RM being close in strange ways, both from an outsiders perspective even pre-slash without noticing it themselves as well as in private.
Reigen being utterly devoted to Mob in the most insanely casual way. Mob being devoted back in a somehow entirely different but just as sincere way.
Reigen teaching in any way possible, I love everything where he instructs Mob & I love that there's so much of it!! Teaching him in bed, teaching him how to shave, tie a tie, how to cook, where to buy to get most of one's money, how to apply for jobs!!! Everything!!! And in the very most cases it's not unsolicited, Mob looks for advice in Reigen more often than not, still well in his 20s. Except for the Yakiniku incidence, Shishou's advice has never failed him.

My fav SasoDei tropes are they are fucked up and doomed lmao. And very obviously I'm #1 aging-Deidara-down fan... Gotta make use of that age gap.
SasoDei is hard to pin favorites down to even more, because I've been in this pit for 15+ years and probably rotated these blorbos through each and every trope I ever enjoyed. (and they are at fault for so many of my fiction kinks...)

But I realize I like a lot of the same tropes but in a contrary flavor for these two ships...
ReiMob devoted codependency that is questionable but so so sincere at its core vs SasoDei codependency in the most unhealthy obsessive way possible
ReiMob loss of boundaries because they're just too comfortable around each other vs SasoDei loss of boundaries because both or one party are forced to
~15 year age gap as a "against all odds" in ReiMob vs "it's even more fucked up than it sounds" in SasoDei
Reigen taking care of Mob because he decides to, because that's kind of his calling and he thrives doing so and he's so good for that kid vs Sasori taking care of Deidara because he has no other choice and he's fucking awful at it, even in the cases where he genuinely tries, he fucks this kid up so much worse than he already is
Reigen teaching Mob in all those lovely aspects vs Sasori raising Deidara into a child soldier (& tangential other ship, Jing Yuan & Yanqing a bittersweet spot inbetween these two)

Sexual trauma is a noticable trope fav for Deidara exclusively tbh, both inflicted by npcs for Sasori to deal with or by Sasori himself... That's smth I'm not really into in RM.

That said, I think I often make it seem like I don't ever wanna see SasoDei happy, but I love all the angst & suffering and killing one or both of them off, but inbetween all the doomed things, they also have immense power couple potential, which is a trope I will always adore about them!!
They are two bad bitches & even in instances where they're bad for each other, they will always be two times worse for anyone who'd dare mess with them & I think that's very romantic <3