Manga where the party receive a bag that only activates because the protagonist is deceased

Question

The main plot point I remember is that, in an early scene, the protagonist is found peeking at the party members. The party consists of the main character, who is male, and three females: a mage, a priest, and a fighter of some sort. Then, the party members realize the protagonist is gone and search for him, but to no avail.

Suddenly, a bag or something similar arrives, containing a letter of recommendation and other items to help the party. The bag uses his magic that activates when he dies. The mage is the first to realize this fact, and they discuss how the protagonist didn't always behave this way; it was a recent change. They finally realize he pretended to be a pervert on purpose to make them avoid him so he could fight the demon lord alone.

They search for him in the demon lord's domain, only to find a huge crater and a sword. They cry, realizing he insisted on going despite knowing the risk and that he would die fighting the demon lord. The scene is similar to overly cautious hero final battle where he was leaving to fight the last boss alone.

Answer 1

This is Kiraware Yuusha wo Enjita Ore wa, Naze ka Last Boss ni Sukarete Issho ni Seikatsu Shitemasu!.

The hero Ares was about to fight the final battle for the fate of the world. However, the three party members who became his friends on the trip said, "I can't follow you anymore!" Yes, he was hated by all the party members. Their patience had run out and they finally left Ares. But that is what Ares, the hero, wanted. The last opponent is the genie [Demiurge] who is bringing destruction and chaos to the world. He cannot involve his party members in a fight from which they may not return alive. So it was his plan to play a disgusting person who would drive everyone away from him.

The question describes the events of chapter 1. The protagonist and his three female party members are going to fight the demon lord Demiurge. They refuse to continue due to his perverted antics and return to the inn, leaving the protagonist to fight the demon by himself. The "peeking" scene mentioned was a flashback.

At the inn they discover some items he had left behind, tailored to their wishes. This does include a letter of recommendation:

And it does explicitly mention magic that activates when the owner dies. From this they determine that he was acting as a jerk specifically to chase them off so he could sacrifice himself in the final fight and not involve his party members. They return to the demon's lair and discover a sword in a crater:

While not mentioned in the question, the protagonist survives this and basically starts living with the demon he just sacrifices himself to defeat, who proclaims herself his wife.