Allow me to explain,
MC's Personality :
He's been considered a failure. 'Disqualification' is the word. Now he isn't going to take up rapid motivation after getting isekai'd into a fantasy world. However, he does find a reason to live. His motive is to commit double suicide with his lover, whom he suspects of getting teleported to the same world as well. There are negative vibes and he remains unfazed. Dazai is non-serious throughout the journey, at least how far i have read. I love the lightheartedness that comes along with sweet humor.
Plot?
It begins with the mc wanting to commit double suicide with his disciple-lover. After getting summoned as a hero, he leaves the summoner and attempts to kill himself multiple times. However, the story contains this 'unable to suicide' premise, where he fails to take his life in the beginning. A 'poison' in his body will harm whoever tries to attack him. Again, unique element and i'm enjoying this! Then there is the presence of multiple other heroes (other-worlders) who play the role of antagonists.
Side characters are cute, their impact is not very huge on the main character and add to the humor. These are generally fantasied or straight up generic. (Elf, Cat-girl, Demi-humans) Character designs are decent, and art of the manga is a plus point.
'The choice of how i should live my life, was not something I ever left to others.'
^ A really positive quote and makes up the main character's attributes. Most of his development has come from his previous life.
Also note, this is 1948, he probably is unaware of existence of magical creatures like elves. This provides a clean contrast into the perspective the main character sees the new world. There are a lot of historical/lifestyle references from the early 20th century era.
Humor is sweet and lighthearted, this is maintained really well throughout the manga. The confidence of the main character comes from being unfazed and reacts instantly in a surprising manner.
P.S.
-"Shinjuu" means the occasion when two-lovers try to commit double suicide in order to show their unchanging love for each other.
-June 13, 1948 is the actual date of Osamu Dazai's dea
