Do you want to punch God in the face? Want to do it with one of his own? Do you too want to have a kickass robot angel fight by your side? If so, this guide is for you! I'll be detailing what you need and the fusion process to acquire the ultimate Seraph, Metatron!
Now, you may be asking, "Why should I fuse Metatron? My Daisoujou and Trumpeter are great, and I can just Focus+Freikugel."

While this is true, being the ultimate demon of the Seraph family has a few strengths that set him apart and make the grind worth it. For starters, he's the only demon with the Fire of Sinai skill which inflicts massive almighty damage to random foes. While the random aspect may seem lackluster, this means it can actually hit a single target twice. Useful for bosses. Second, he actually has hidden resistances to Physical, Fire, Electricity, and Force attacks, which means he takes half damage from the previously mentioned attacks.

A note before we begin: While it's easiest to fuse him following the True Demon Path, Metatron can be acquired in different endings. Simply complete the Labyrinth of Amala AFTER you enter the Tower of Kagatsuchi.

These are the requirements to fuse Metatron. All must be met before he may be fused in the Cathedral of Shadows. They are as follows:

1. Metatron must be beaten first. Therefore, you have to beat all the other fiends to get the Candlebras, get the Star Key from the Manikin, and journey to the 5th Kalpa to slay him.


2. You need to be a high enough level. You have to be level 95 to even fuse him, and that's assuming you aren't doing a sacrificial fusion. If you need XP it's recommended to set your difficulty to hard for better drops/more frequent encounters in the DLC dungeon, "Where the Demi-Fiend was Born". If you don't have or won't buy the DLC your only other option is to set the game to merciful for triple exp/macca and grind up at the Tower of Kagutsuchi.

3. You'll need/want a lot of money. Fusing Metatron is a process to say the least and grinding at the Center of the Conception will help out a lot with this. This can be easily done in hard mode at the DLC dungeon, "The Center of the Conception". Sell the bulls you get for ridiculous amounts of macca. Otherwise just turn on merciful and farm. Both of these methods are sped up with instant kill skills such as Beelzebub's Death Flies skill and Trumpeter's Evil Melody.

4. It's recommended to be at the Tower of Kagutsuchi 3 (depicted in the map to the left). You'll need demons from here and the Cathedral of Shadows is right across from an Amala Terminal, perfect for sacrificial fusions.

5. Record ALL demons you get in the compendium. If you lose one or get a fusion accident you'll just have to reload your save instead of finding the demon again. Furthermore you'll be re-summoning demons so saving them and having the earlier mentioned Macca is recommended.

Also, just as a convenience for the reader I'll be bolding demon names which will be written after their race, e.g. Divine Dominion.

1. Starting off, get a Divine Throne . It evolves into the Seraph Uriel. Throne is found in the Tower of Kagatsuchi.

2. Fuse Uriel with Divine Dominion to get the Seraph Raphael. Dominion is located in the courtyard at the Amala Temple, where the three pyramids are visible.

3. Summon another Throne and fuse it with the Seraph Raphael to create the Seraph Gabriel.

4. Summon Raphael and Uriel, and wait for a full Kagutsuchi. Fuse the previous two as well as Gabriel together in a sacrificial fusion to make Michael. Fusion order or the sacrifice does not matter.

5. Acquire any Divine (like Throne) or Seraph (Uriel). Divines are at the Amala Temple courtyard, or alternatively you could just summon a Seraph out of the Compendium.

6. Get a Tyrant (Aciel, Loki, Mot, Abaddon, Surt etc.). Loki is found in the Amala Temples.
6a. If you're on NG+/next cycle it's recommended to do some additional sacrificial fusion to fuse a high level tyrant to give Metatron a huge stat boost.
NOTE: You can actually sacrifice such a high level tyrant that Metatron will reach LVL.255 and will be unable to level up, making it impossible to get Fire of Sinai on this particular Metatron.


My example high level fodder Mot pictured below.
7. Start your next fusion on a full Kagatsuchi, fuse Michael and the Seraph/Divine and sacrifice the tyrant.

You have now fused Metatron!

While the process is by no means easy or short, the end result is definitely worth it. With skills such as Fire of Sinai, Megidolaon, Debilitate, Makakaja, Tarukaja, and Victory Cry in his skillset by default, Metatron is a fantastic demon to fuse and will do God's work on the demons (and God too I suppose). Also, I sacrificed certain demons to grant Metatron certain skills. Some examples are Prayer and Avenge, to add to his support potential while still being able to potentially counterattack to even out half of his skillset now being support. With Tarukaja at stage four, Metatron is capable of dishing out some pretty nasty counterattacks.

Naturally, as with any demon, it's recommended to level them up to level 255, and especially with Metatron. Three of his moves cost 50MP and one costs 48MP, with the buffs costing only 12MP. However, dealing any magical damage will wear down his MP if the match doesn't end so Victory Cry can kick in or if Demi-Fiend intervenes with a chakra item.




Resources

Game8 for the blue outline images of demons:
Team, G. (n.d.). Metatron skills, stats, and Fusion: Shin Megami tensei 3: NOCTURNE (smt Nocturne)｜Game8. Game8｜The Top Gaming and App Walkthroughs Straight from Japan! Retrieved September 9, 2021, from https://game8.co/games/Shin-Megami-Tensei-III-Nocturne/archives/333720.

Megami Tensei Wiki for images as well:
Megami Tensei Wiki. Fandom. (n.d.). Retrieved September 9, 2021, from https://megamitensei.fandom.com/wiki/Megami_Tensei_Wiki.