Interesting concept. The author manages the rules of the time loop well, being consistent throughout the whole manga. Characters are two-dimensional; they feel more like an idea/archetype than actual people with motivations, with a few exceptions.
The plot, as stated before by others, mostly follows a logical path. However, there are quite a few plot holes. In some of them, I guess you could try to do mental gymnastics to justify them.
Examples:
-The glasses girl somehow survives having her head smashed with a rock multiple times, but it felt more like a plot device to make Nee-chan get caught.
-The MC escaping after killing his dad too, (since he went for the trouble of putting the detective's fingerprints in the knife, besides, the whole situation could have been explained as self defense..come on, the mf made a false claim that he planted a bomb) but mostly how ridiculous it was for the detective to still have credibility after kidnapping the suspect and making false claims (there are more things, but I don't remember clearly).
-The mere fact that MC was a suspect. The author develops this a bit better later (I like how he put together what happened when the handcuffs disappeared), but the way the detective got suspicious of him doesn't convince me.
-Other instances like the nurse somehow concluding that MC was the killer just because the police were investigating her sister, when the logical conclusion would be: "Oh, the murderer is going after MC's sister!" no matter how unstable she was.
In the final chapters, there was a heavy lore drop that felt really rushed, and there wasn't an adequate ending. The whole premise of the story was "This boy has to kill so his sister lives" but we don't even get an answer if the operation was truly successful, nor a reaction to the whole mess.
I dont have a problem with a character having a sad ending. However, it was truly unsatisfying; it seems like no one in the police (who knew of the time travel) could understand that MC didn't have a choice in killing, most of the victims were horrible people, too. Of course, this is addressed slightly at the end, but just a few dialogues don't cut it; it is not a matter of sympathy, but of logic: "If this person doesn't murder someone, all of humanity is doomed to repeat the same day".
In the end, what remained was a character who suffered throughout the whole story and didn't even get to see if he accomplished his original goal (saving his sister). We, as well, didn't have this luxury. Like his whole journey was meant for nothing.
Conclusion: The detectives were annoying, and there wasn't enough exploration of MC's family (mother's backstory doesn't even make sense to understand her actions completely). The characters felt like plot devices, wasted potential. MC's journey felt like a waste.
6-7/10. It has some brilliant moments that make it a worthy read. I wouldn't call it generic, but definitely not something really deep, and the plot is predictable. Works like Re: Zero, Death Note, or Stain's Gate are a bit similar and develop some of the dynamics presented here better, although I like how the Time Loop works here.
Good ideas, but execution is insufficient.