In my case, a thing i forgot to mention, but in the panels where Reiji was standing still with a curious gaze, looking at the 4th wall while Gen and Chako kept walking in their peaceful and unkempt town, like looking at a shellshocked Nagi (and considering all things, Nagi may not even be her real name) who never looked away from the destruction and chaos may have a symbolism and metaphor of Reiji entering to her heart and wanting to know more.
Most of us know Nagi feels like nobody loves her since ch16 by comparing Reiji's situation to hers, and this chapter only confirms that. Maybe Nagi's reasons to die are because she wants to meet her family and friends in the afterlife, survivor's guilt they say.
While Reiji's reasons to die are because he wants to run away from a love already confirmed as false (Mom used him as a sub and made others hate him so Reiji would never leave her, not out if love, but of him being the vessel of her hatred towards everything, Gen wanted to be Yuko, Chako used him as an instrument that would guide her to Esemori and took their friendship for granted and Yuri... Yuri just wants to catch up with her lost teenage years using him. Not surprising he wants to die.
The point of the flashback may also point at Nagi finding out Reiji may only have had everything she lost on the surface, but, on the substance, he also started to lose that thing since the moment Yuko's dad died, that was the moment Yuko started to chain Reiji to herself, with every attempt from his closest relatives (Hermano's family, Kazu) making Yuko cut ties with her bro for good, turn Masaharu against Reiji and traumatize Gen. A common ground despite of their opposite realities: one had everything, but nature stripped those things away from her, while the other basically had nothing in substance, despite of physically having it. And the people who want to help Reiji doesn't know the core of his suffering, that's why Reiji considers them as dazzling people he can't take their hands.
The most surprising thing is that Yuko never tried to get a clutch into Chako, although it's known why: her family despises the Kuroses, so it would have been useless and would have had the cops involved, that's why Yuko used Yuri as an instrument to keep a leash on Reiji instead, and she, unless Reiji mans up, is succeeding if we go by the fact Reiji is engaged.