The manga starts like an isekai story, where the main character is sent to a different world. The main character meets a priest and stays in the church. With the help of the priest he live peacefully. Then he meets a girl and they start investigating something. Because there is something evil near them or something like that. In the end, if I remember correctly, the priest is dead. Not sure he is good or evil but they find a vampire in a mansion. They try to fight the vampire but it is just too strong. The girl pulls out a sword from between her breasts and gives it to the main character. The main character defeats the vampire with this sword. The chapter finished here.
Answering questions form comments:
"The chapter finished here." - was this all in the first chapter?
I think at the time I read the manga, there were about 3-4 chapters available. But it has been around 3-4 years since then.
Hi, welcome to the site. Was this in full colour or mostly black & white? And do you recall the hair colour of the female lead?
The manga was completely in black and white, except for the cover which was in color. I don't remember the exact color of the girl's hair, but I think it might have been brown. I'm not entirely sure though.
I don't want to mislead you guys, but when I was reading it on the mangar*ck app, I constantly confused it with the manga on this cover. Although their topics are not similar, I'm almost certain that they were released around the same time and cover images also resembled each other.
(Makenshi no Maken Niyoru Maken no Tame no Harem Life)
Edit: In addition, the reason why he was investigating something bad was because of this girl. The girl was some kind of adventurer or someone who hunted these creatures. I don't think the girl was expecting to find a vampire in the mansion, but I'm sure she was searching for some kind of evil entity. During the fight with the vampire, the main character was destroying the walls of the mansion. Although the girl was surprised, they are not strong enough to defeat the vampire. After a while of fighting, they couldn't beat the vampire. They tried to escape to the main entrance of the mansion, but the vampire caught them. As a last resort, the girl pulled out the sword from between her breasts (like Raiden from Genshin Impact). It was a sort of magical sword. With this sword, the main character fought against the vampire. He managed to defeat him but barely. The girl had to travel with the boy because she had to give the sword to someone she chose. When they started their journey, the manga had no continuation from where I left off.