I have seen it, I'll see if I can dig up where

No, can't find it, even on a couple of Japanese sites that go pretty deep into detail with the formula. I'm pretty sure that a couple of old FAQs have been taken down which might explain what happened.

Haha, I found it on that site, it's just spread over a couple of pages


A characters base purification power is:
Purification Power = Level +9
Increases by 20% if you have the
skill "Purification Power +1". ＋2、＋3... As it increases, it increases by 30%, and at "Purification Power +10", it quadruples.

(The recruiting power is )

Purification power in normal purification = Original purification power - Level difference from the target × 2 (if the target level is lower, it will be added up to +10)
Purification equipment, purification power with baptismal attack = original purification power
Unique skills with
a purification effect, light blue local purification and great miracle purification power have not been investigated.

The cumulative purification power required before "No, but I feel like becoming a friend" is as follows.

Cumulative Purification Power > Purification Difficulty× (Lv+4) × 3+30 (However, boss systems
(Hecatoncale, Crowbar, etc.) are 150 regardless of level.) (
If it exceeds 1/5 of the required purification power, it will say "I'm a little interested in this ~", if it exceeds 2/5, it will say "I'm wondering if I want to become a friend", and if it exceeds 2/3, "I heard that I want to become a friend" will be displayed.) Purification

difficulty ( Kal's note - the monster names here are all direct google translations of the Japanese but you can get a pretty good idea here)
1.0 ... Petit Komori
1.5 ... Zomby, Hanahana, Eringya
2.0 ... Powerful Zomby, Minidora, Big Bat, Big Bear, Mu-san, French Kiss, Ganchan, Hitodama, Obake
2.5 ... Stamina Zomby, Choo Choo, Gabri, White Devil, Mokkosu, Beautiful, Kraken, Onibi, Yurei, Kumatan, Siren
3.0 ... Zomby Knight, Golden Bat, Vampire, Ogre, Hipopotasu, Mandragora, Moby ♥♥♥♥, Salamander, Fusafusa, Pumpkin Head, Ghost, Eringer, Kumapu, Undine
3.5 ... Nosferatu, Behemoth, Rafflesian, Leviathan, Javaok, Phantom, Dugong
4.0 ... Wasawasa, Jack Lantern, Elinder, Lamia
5.0 ... Halloween
6.0 ... Pumpkin King
8.0 ... Ellinger
10.0 ... Zom Beaking Hani
12.0 ... Gnemurin, Red Cap, Basket Case, Boxed Devil

Examples.
Petit Komori (Lv1) ... 45
Gunemrin (Lv9) ... 497
Zom Beaking (Lv500) ... 15150
bar (Lv2000) ... 150
If you have a demon of
the same species as your companion, the cumulative purification power required is doubled or tripled... And so on and so forth.

I think that means that

Purification Power = (Level + 9) * (1 + P0 + (N-1)*P1 )

where P0 is 0 if you don't have Purification 1 and 0.2 if you do, and P1 is 0.3 and N is your Purification Power - 1 . Unfortunately I'm not sure what the quadrupled at 10 is.

At Rank 9 the adjustment should be (1 + 0.2 + 0.3 * 8 ) = 3.6 , but I'm not sure what quadrupled means for rank 10. Since what is quadrupled is ambiguous, intuitively I'd be incliend to think it's 1 + (( 0.2 + 0.3 * (8 or 9)^) *4 ) . On one hand that's a much larger gain than you'd normally see in the Disgaea-verse but on the other La Pucelle is weird in a few places since it's such an early game.

^depending if the 10 counts as an increase or just multiples by 4.