You can go to the church at any point in the game after chapter 2 begins.
Chante
"I'm sorry. We made a mistake."
Priest
"Wait, wait! Wasn't there something you came to church for?"
"You were looking from outside this church-like place and it looked like you intended to enter."
"No, no. This is a church."
Chante and Elise step forward again.
Chante
"I knew it. I thought this was a church."
"We'll stay for a while, so we can go and greet the priest, but..."
"Where is the priest?"
Priest
"He's right in front of you. I am the priest. Nice to meet you."
Chante and Elise step back again.
Chante
"I'm sorry. We really did make a mistake."
Priest
"Wait, wait! Hey!"
Chante and Elise step forward again.
Chante
"In what world is there a muscular Buddhist priest that acts as a Catholic priest?"
Elise
"Nee-san, you're being too forward..."
Priest
"Hahaha! Well, that's the reaction I usually get, but..."
"For the time being, I'm an authentic Catholic priest. Nice to meet you."
Chante
"Hmph, even though you look like that. Well... you appear to be the current priest for now."
"I'm Chante. There's a little reason why I'm like this, but I was formerly human once."
"And this is my younger sister, Elise."
Elise
"Nice to meet you, shinpu-san (Mr. priest)."
Priest
"Yeah! If there is anything bothering you, you can come visit at any time."
Chante
"Hm? That's a very nice thing to say. What do you do exactly?"
Priest
"I provide information about places to adventurers. To be exact, information about secret treasures."
Chante
"What!? You'll tell us?"
Priest
"However, it's not free. It's necessary to fix the appearance of the church."
Chante
"It's somehow related to gold, isn't it?"
Priest
"Yeah, you have a good understanding, but it's not gold that's needed."
Chante
"Not gold? Then what would be a good donation?"
Priest
"You pay with your body."
Chante and Elise step back quickly, surprised by the priest's statement. Chante becomes angry.
Chante
"Elise's chastity is in danger!"
Priest
"No, not that. Not that. You contribute with your max HP."
Chante and Elise step forward again feeling a bit relieved, at least, Chante is.
Chante
"So in exchange for Elise's max HP, you'll teach us about the secret treasures?"
Elise
"As I thought. It has to be me..."
Priest
"Well, that's how it is. You can contribute with any surplus HP so you still have enough left."
Chante
"I see, because adventurers raise HP too much."
Priest
"I'm not saying to overdo it; but think about if you feel like it."
Chante
"That's true. We'll think about it if we need it."
Priest
"Yeah, I'm counting on you."
Elise
"... What about my opinion?"
Since all of the treasures are listed in this guide, as well as how to obtain them, the hints will not benefit you any more than the information in this guide.
However, if you prefer to approach the game not knowing exactly what to do, but rather work off a riddle, you can read on.