The Demon Lord Act

The Demon Lord Act is the first episode of the How NOT to Summon a Demon Lord series. It aired on July 5, 2018.

Synopsis
''Takuma Sakamoto an ace player of the MMO RPG Cross Reverie is summoned to an alternate universe as his MMO Character Diablo. Because of a special ring his character wore that reflects all magical spells that are cast on him. His summoners have slave collars placed on them who originally planned to have put on Takuma himself. Because of his awkward nature being a shut-in Takuma changes his name to Diablo and acts in his character's persona. Now Diablo is stuck in the world that he once was an ace player in and has to survive in it while also being roped into a dark conspiracy involving a sealed Demon Lord.''

Plot
A brief explanation about Cross Reverie is given and Takuma Sakamoto introduces himself and his MMO character Diablo as the "True Demon Lord" in the game. Without warning, he's summoned to an alternate world as his MMO character and his summoners then each kiss him on his left and right cheek. Astonished by his predicament, Diablo's summoners an Elf and a Pantherian debate who summoned him. Both believe they were the ones as they followed the summoning ritual procedures including the kiss. Upon learning this, Diablo is left awe stricken that he was kissed and regrets not enjoying it further. As the two summoners continue to debate whether who summoned Diablo and unintentionally reveal to the curious Diablo that he's at the top of a large stone tower known as the Starfall Tower. Approaching the bickering ladies, Diablo realizes that for the longest time he's never really talked with anyone all of his life, which leaves him in quite a predicament. Therefore, Diablo decides to act in his MMO Character persona and then addresses the two in a haughty manner, ordering the two to shake hands with a smile. Initially hesitant to do so, an overwhelming power forces the two to obey Diablo's command. After this is done, slave collars appear on both of the summoner's necks, which astounds all three of them.

At the bottom of the tower, the trio walk and talk about the failed ritual. In it, Diablo realizes that his Demon Lord Ring, reflected the Enslavement spell onto his would be enslavers. Detailing to his summoners that magic has no effect on him, the group head to the nearby town to dispel the enslavement spell on them. The Elf realizing that she and her companion haven't introduced themselves to Diablo, she introduces herself as Shera L. Greenwood an aspiring Adventurer. Her companion, the Pantherian introduces herself as Rem Galleu and she seeks to improve her skills as an adventurer. Being labeled as a rare summon creature, Diablo denotes that statement and not wanting to reveal himself as a shut-in, he proclaims that he's a Demon Lord. Hearing this impresses Shera that she managed to summon a Demon Lord, which annoys Rem sparking another argument between the two. This is stopped by Diablo who snaps at the two and they then continue forth to the city.

Reaching their destination of Faltra City, they check-in at the Peace of Mind Inn where they're greeted by the bubbly inn keeper Mei. Nauseous over being in what he considers a "large crowd", Diablo is further shocked that Shera wants to register a room that's shared with Diablo. The reason behind this is due to the lack of funding they have and Rem chimes in insisting that Diablo stay in her room as she was the one who summoned him. An argument sparks between the two and they're stopped by Mei who threatens to throw them out. It's then revealed that the three of them will share a room with a single bed. Contemplating his predicament over the use of a single bed, a woman acquainted with Rem named Celestine Baudelaire and her two followers enter the room. Diablo recalls the name and Shera states that Celestine is the head of the Mage's Association. Remembering Celestine's or Celes as she wishes to be called, is a prominent figure in the Cross Reverie game as the one who maintains the barrier in the city. Celes' initial motive was to talk with Rem, however, seeing the slave collars on Rem and Shera's necks along with Diablo being there, she states her curiosity about their situation.

That night at the inn's cafeteria, Celes is brought up to date with everything involving the failed enslavement ritual. She's also informed that Diablo is unable to dispel the enslavement cast on them. After Celes realizes she'll have to research from scratch about a way to dispel the slave collars around Shera and Rem's neck. Diablo asks in an authoritarian manner about her business with them, which causes a rebuke from one of her followers named Galluk. Although internally Diablo is frightened by Galluk, he gives a menacing retort that irks him and is also reproved by his superior Celes. The subject then changes to a brief conversation between Celes and Rem who declines having more bodyguards be assigned to her despite Celes' well meant intentions. With that settled with, Celes' party leave for the night and Diablo asks Rem about her relationship with Celes. Rem refuses to speak about it and Diablo has an epiphany that Rem's secret is related to an important main story event that's best to learn about it before hand to avoid a preventable disaster in the future. Grabbing Rem and placing her on his shoulder, Diablo takes her back to their room to "torture her".

Back in their room, Diablo "tortures" Rem in a light and innocent manner until she finally confesses her secret to him. Rem reveals that she has the Demon Lord Krebskulm sealed within her body and Diablo recalls the Demon Lord as the strongest boss in the game. Stating that she wishes to release and extinguish Krebskulm's soul from her body, Diablo then details doing that would kill Rem in the process. Furthermore, he deduces that Rem's relationship with Celes is because of this goal of hers and that Celes is the only one privy to Rem's predicament. The sealing of the Demon Lord is also hereditary as Rem's mother had Krebskulm sealed in her body before she died. Fully aware of Rem's predicament, Diablo vows to help Rem, which gets her emotional as Diablo won't leave her because of her condition.

Afterward, Diablo goes on a excursion around the town while reflecting on how he's done everything all by his lonesome due to his nature. Eventually, he's approached by Galluk and his colleage's from the Mage's Association. This leads into an altercation between Diablo and Galluk who summons a level 30 Salamander. While Galluk boasts and threatens Diablo about his summon, Diablo notes that while impressive, its level is way too weak. The Salamander then belches a blaze of fire at Diablo who walks out of it unscathed. Panic-stricken, Galluk orders his summon to incinerate Diablo and the Salamander fires a massive flamethrower like attack from its mouth. However, the attack still has no effect on the level 150 Diablo. Equipping his wand, Diablo then casts Explosion that eviscerates the Salamander. Approaching the con-fuddled Galluk who demands to know who Diablo is, Diablo answers that he's a Diablo, a Demon Lord from Another World.

Characters In Order of Appearance

 * Takuma Sakamoto/Diablo
 * Rem Galleu
 * Shera L. Greenwood
 * Mei
 * Celestine Baudelaire
 * Galluk

Differences from the Light Novel

 * The episode teaser, which covers the Prologue and bits of Chapter 1 of the first Volume, has Takuma narrate instead of an unseen narrator.
 * The sorcerer & healer couple were given names; Michiko LOVE (ミチコ LOVE; the male sorcerer) & RYO's Wife (the female healer).
 * Mentioning of the 《Wedding Ring》 is omitted.
 * Mentioning of how Takuma got 《The Demon Lord's Ring》 from the 《Demon Lord of the Mind, Enkvaros》is omitted.
 * Takuma instantly knew he became Diablo instead of Rem and Shera saying aloud at the same time claiming to have "summoned Diablo."
 * Rem and Shera learned of Diablo's name after he talked instead of them knowing the name before they summoned him.
 * Diablo was informed that he was on Starfall Tower when Shera mentioned that she was the one who recommended that she and Rem go there instead of Diablo deducing on his own.
 * The narration informing about Summoners and Summons is omitted.
 * The part where Rem and Shera trying to command Diablo to see who summoned him was omitted.
 * The part where Shera and Rem were about to fight with their bow and Summons respectively was changed to simply arguing.
 * The location of the talk of the Enslavement Ritual and it being reflected was changed from still being in Starfall Tower to outside.
 * Diablo demonstrating his Elemental Magic to the girls was omitted and changed for the next episode to be the one when the girls find out he could use it.
 * Explanation of how Diablo use the game descriptions of the spells to invoke the magic is omitted.
 * The trio crossing through Fort Bridge Ulug to Faltra City is omitted.
 * Meeting with Boris Marcus is changed to when Diablo and Shera are delivering provisions to the Bridge of Ulug (their second day of being adventurers (episode 3)).
 * The fight with the drunken Mages and Diablo was changed to Galluk being the only aggressor.
 * Diablo defeated the 《Salamander》 with the spell 《Explosion》 instead of a physical attack.
 * Due to the other Mages not summoning their 《Spirit》 Summons of different elements, Diablo did not defeat them in one attack when trying to determine Elemental affinities.

Differences from the Manga

 * When thinking about how he "talked to girls before", the manga had two Cross Reverie players, whereas the anime only showed one.
 * Diablo's imagined cohabitation scenarios, one with Shera and another with Rem, which are both set in his world, are left out.