I ain't calling you a liar, but i'm going to need more than just a claim you did it, depending on your build, either Nakano will kick your ass physically, or the twins will shred your resolve. Without decent gear and good ability combinations, i can't imagine how you could accomplish it, and as i said, acquiring the gear will net your more than enough experience to bump you over level 5. Also, with no consumables, your chances sub-5 are even less since you can't get Cait to heal you between fights and one often ends a fight with less than half health on at least one character regardless of build, meaning the next fight is even more difficult. I'm not saying it's impossible but... fuck... explain how you did it and how many attempts it took you. Sure you didn't have the game on easy mode?
Looking at my spells and stuff, at the time the strategy I used was DPS-focused. I had Cait and Berwyn in my party and I was basically a Berwyn, so the amount of damage we could dish out per turn was quite hilarious.
Unfortunately I don't have a save from right before I entered the dungeon, only one from after the dungeon where I had basically just recently leveled up, probably from clearing the dungeon itself.
The gear, though? Well, I don't have any idea what you mean by that. I am literally wearing the Witch Corset set that I got like 10 days into the game and was using the Spiraled Staff from the Berwyn quest, something I also did extremely early in the game. I actually just beat the entire Winter City using almost the exact same set, but with rings and a different collar. In my old save I'm not even wearing a belt nor rings, though I do have Kiyoko's necklace which provides some nice resistances. The setup I used to take out the dungeon is very weird and I'm a bit surprised I didn't have more difficulty doing it. I have Withering Bolt, Grease, Fireball, and Summon Kiyoko. You can do some absolutely nasty damage by Greasing a target and then smacking it with a Fireball, and if I recall correctly Fireball acts as an AOE if you grease all targets, meaning you can get a nasty hit off on multiple opponents. In between Grease and Fireball I would just spam Withering bolt and combine that with Berwyn's own at-will, we could deal over 100 damage minimum per cycle and close to 200 damage with a lucky crit thrown in there. I wouldn't really call the build optimal at all, though. Could definitely be improved, particularly on the gear side. Stats are a bit of a mess too, I initially was going to go for a Courtesan run so focused on sexiness and stuff like that before giving up and going for a sort of Archer build... before giving up and going White Mage... before giving up and going Black Mage. Any good statistics are completely by accident.
I went through the dungeons with some other mixups and I found it was a lot better to just not have Summon Kiyoko as usually if the Golem died things were going horribly wrong and I was probably dead anyway (sidenote, there were a couple fights Kiyoko did win for us with her debuffs but I think it was mostly luck), and replace it with a damaging move of some kind. Also tried it with using Heal instead of Withering Bolt and I found it turned the dungeon into a case of "death by thousand papercuts" where we would slowly kill the opponents faster than they could actually kill us, but since it relied on Berwyn doing most of the per-turn damage I recall losing a couple of times due to bad move choice by the AI. No, Berwyn, we don't need a group heal to heal a whopping 10 damage between the three of us. Kill the enemy instead please.
From what I can gander I think I got good RNG on the fights, stuff like Cait healing me and Berwyn on the right turns, dodges, or the enemy picking moves that were... not really the best. Getting some good criticals on the enemy and not getting critical'd in return and so on. I remember I also went through the dungeon after leveling to level 5 and I recall Banished being ludicrously useful, it is basically a oneshot to Golems if you're having trouble there and it can take an enemy out of the fight for two turns, giving you time to heal in single-target fights and letting you absolutely pound the living crap out of whoever is left in the dual fights.
I actually still have the level 5 save from where I made a hard backup before trying the dungeon again at level 5. I probably should've done that before doing it the first time too, but I usually use two save slots (one as a backup, one as a main one) so I only really end up making hard saves to the drive when attempting something unusual and they have long since been overwritten.
Maybe the fight has gotten more difficult over time or something? I haven't done it in a loooong time... I ought to toy with my old save a bit more and see how well I can run it. It is technically modified, but all I did was give myself fox berries to turn myself into a fox (am not a sadist and am not going to grind for 50 days for like 6 berries lol) and a bunch of money for Nursery upgrades. I don't even think I spent it on anything except the Quarterstaff for Kinu, Training, and a nice pair of stockings and garterbelt, not that I'd had it for very long prior to doing the quest anyways and never used tease at all during the quest.
Edit: Oh! This is also kind of important, I recall trying to stall a couple fights out a cycle or two in order to make sure everyone was tip-top on HP for the harder fights like Nakano and such, although it was pretty successful when I had the healing spell, it was a bit less so for Cait healing as I had no real control over it.
And, the amount of attempts it took to beat all the bosses from the start was... probably 4 or 5 in order to get to know the bosses and beat them, but the overall amount of runs I did was probably more similar to 10 in order to get all the defeat scenes and test some other spell combinations and such. I actually remember looking at my gear after all was said and done and going "You know, that would've probably been a lot easier if I actually had paid attention to my gear at all." and proceeding to forget to change it until I went for a Winter City run recently.