At the end of volume 1, during the accusation event, MC plays uno reverse card on him and after being cornered, Amada shows a part of his true self and lose his place in the classroom, and he even take a leave of absence.
He returns in volume 2 with a new plan thanks to another childhood friend named Hitsujitani, but at the end the plan failed, and Hitsujitani saw for herself Amada is not the kind guy she thought he was. Besides he was unaware his ex friend and harem members played spies for MC.
In volume 3, Tsukimiya Ouji is forced to play the douchebag and MC tries to figure out what happened, Amada takes the chance and tries to play the hero but got shotdown by Hidaka.
In volume 4, Amada is mostly absent, but at the end, he suffers another humiliation when a 3rd childhood friend shows up. He thought he could use her but unfortunately, she met MC during summer break and she learned what Amada is. When they met again, she saw right through him and let him dumbfounded.
In this volume, we also have his POV from the 1st timeline and the guy is so messed up he led this 3rd childhood friend to her death only to make her twin sister his pawn.
So in short : Amada is humiliated by seing MC and Hidaka being close, the lost of his harem, his plans being wrecked, and he even had to spend his summer vacations with the introverts group instead going to the beach with beautiful girls. For a harem romcom protagonist, it's a hard reality.
I'm waiting for a bigger comeuppance but seeing him humiliated like this is pure joy
I think if you put some effort to tie in all the hints from first timeline, I’d like to think the real villain suffered MUCH, MUCH WORSE as their own karma caught up to their actions. There were many plot points that heavily implied that their actions, ESPECIALLY the final escalation that ultimately led to Kazuki and his family’s death
ultimately made Amada lost trust among most (if not all) of his heroines, and led to multiple heroine suicide due to either guilt or their lost of faith in humanity. He was THAT fucked up when then the karma finally hits.
What happened next, I highly believe will be the birth of a villainess that took over Amada’s life (heavily implied to be the VTuber egirl introduced in Vol 2) and manipulated him into her pawn, dooming him in a seemingly eternal toxic relationship with her as implied with what happens to the other guy in the second time line in Vol 3, probably worse.
Which is why when the story continues, we begin to see even more and more reveals from the Amada heroine characters about what happened when their body count starts to increase as they accused Kazuki as a villain
Kazuki’s father (Car crash, from Amada manipulating Tsukiyama’s father into firing him)
Kazuki’s mother (Murdered, from Amada manipulating the twin sister into convincing the murderer)
Ishii Yuzu (Kazuki’s sister) (Car accident/Jaywalking, from Amada manipulating the VTuber girl into bringing false accusations, leading to bullying )
Ishii Kazuki (Suicide by jumping off school roof, due to depression from everything Amada and co had done)
Hidaka Mikoto (Likely suicide by hanging, due to losing faith in humanity and lost of beloved Ishii Kazuki after what Amada had done)
Iba Kouki (the OG glasses villainess) (Also likely suicide by hanging, losing faith in Amada and guilt for tremendous pain caused to Kazuki, out of her calculation)
Souda Hiromi (The dead twin sister who drowned in an accident in Okinawa, due to manipulation by Amada into finding local love legends on the beach during dangerous tides)
Souda Yumi (The surviving twin sister who took over Hiromi’s name) (Heavily implied suicide, most likely drowning herself, due to guilt on her role causing Hiromi’s death and manipulation into doing something terrible by Amada, aka inciting murder on Ishii’s mother that led to his sister’s death and ultimately his suicide)
There could be more but you know what, Amada sure is fucked up… If anything I want that karma to hit across multiple timelines but I believe what happened to him at the end of Vol 4 is nothing compared to the world after Kazuki’s death.