Basic Expert: Begin your Isekai adventure as the Dungeon Boss

You are the Zero level BBEG
Start out as a zero level human. Just roll the six basic abilities. Pick a Japanese Character name. Its Tradition.

Part 1: Grandfather's House
In a secret store-room in your grand-father's house you find boxes of old artefacts and antiques... and at the back of the room, a heavy timber door engraved with an owl, fitted in a free standing stone archway. 

The Room contains books, antique swords, crossbows, armour, walking sticks, canes, an astrolabe, jewelery, outdoors equipment, all dumped in timber chests and boxes. Staring at the owl's eyes grants you the ability to detect magic (3 uses/day) as the detect magic spell. Amongst the junk is a pair of gimmicky ebon horns you can wear on your head that grants you an aura of intimidation giving a -6 penalty to your opponent's Morale check but it also identifies you as the Demon-lord of this dungeon. And a spider brooch that causes hostile spiders to flee from your presence.

Part 2: The Dungeon Beyond the Door
The Owl-door opens into a long stone tunnel whose apparent end vanishes into the darkness. You can see tiny spiders on spider webs here and there.

The door can be pushed open by the PC opening into a long, stone-lined tunnel ten feet wide. The tunnel continues off into the darkness. The spiders are poisonous.

Tiny Dungeon Spider: HD: 1hp, AC: 8, AT: Poison, DA: special, SA: Zero Level Human, NA: 1d4 (1d4), ML 8, TT: V, AL: Neutral, XP: 5xp. Description: anyone bit by a spider will take 4hp damage (save vs poison to take half damage).

Part 3: The Dungeon Entrance
Stumbling out of the dungeon and into the light you see an almost medieval rural village from some Fantasy Anime/Manga and some villagers gathering in a mob. They are pointing at you. A number of them scream in a foreign language and flee while four of them rush toward you armed with burning torchs, forks, and clubs.

The quaint Village of Møkkhaug

The Village
Located off the Imperial highway are three timber and daub dwellings, and a reasonably deep communal Well faced in stone, surrounded on three sides by a poor quality timber palisade. The Village of Dung-pile (Møkkhaug) is a Zero-level shit hole, economically depressed, with little to nothing in the way of interest other than:

• The poorly educated peasant farmers (with nothing in the way of a governing authority).

• What passes for a communal hall where they occasionally cook food and serve what laughably passes for Ale.

• The village Well with its reasonably good water supply.

• The Dungeon of the Demon lord.

The Four NPC Heroes
The Adventurers have every intention of killing the demon-lord and ending the threat posed by the dungeon...

• Thap: Zero-level human; Lawful; 7hp; AC9; S16, I11, W9, D10, C12, Ch12; Clothes, boots, pitchfork (1d6+2 strength bonus); Thap is a turnip farmer in love with the charismatic Rin.

• Mika: zero-level human; Lawful; 6hp; AC9 (+1 penalty to attack rolls on Mika); S12, I10, W14, D11, C6, Ch8; clothes, boots, torch (1d4); Mika is slightly introverted and has poor health. She has good judgement though is often ignored by those with higher charisma. If a party member is injured she will on successful charisma check hold off the Demon-lord while the others retreat.

• Haro: zero-level human; Neutral; 1hp; AC9; S11, I17, W8, D10, C8, Ch12; normal clothes, boots, club (1d4); Haro is an intelligent (speaking common, elf, dwarf, and guild-tongue) villager who wants to be a merchant and is merely aiding to investigate the dungeon for goods he can sell from the guild shop he wishes to open. He isnt keen on dying at the hands of a demon-lord and will retreat if Thap is killed. If he fails a charisma check he will flee.

• Rin: Zero-level human; chaotic; 4hp; AC7; S12, I13, W7, D17, C10, Ch15; normal clothes, shoes, dagger (1d4); Rin is a coward leading this party of adventurers to their deaths in the Demon-lord's Dungeon. She will turn on her companions for survival or personal gain. If she fails a charisma check she will plan to betray the party to the demon-lord offering herself to the Demon-lord (irrespective of the Demon-lord's gender). If Thap is killed she will stab Haro or Mika (if either have survived to encounter the Demon-lord) with her dagger before switching sides. If the rest of the party are dead before encountering the demon-lord she will flee to the village

Demon-lord Victorious: If you the Demon-lord are successful in eliminating the adventuring party you get 3xp per opponent killed or subjugated. The village will pay 50gp to the next group of first level Adventurers to show up and purge the Demon-lord.