Asriel, a returning character from Undertale, is Kris's older brother in Deltarune. He is mentioned by numerous characters in Hometown, but is away at university and does not appear in the game's first two chapters. When home, he lives with Kris and his mother, Toriel, in the northern end of Hometown.
Unlike his sibling, Asriel is more open and friendly to the other townspeople. He is very popular in Hometown, and many of Kris's neighbors exclusively talk about him to praise him, unlike Kris. He also has many trophies on his shelf. He likes music, including religious ska. Despite the differences between him and Kris, he does care a lot about them.
Asriel is the oldest child of Asgore Dreemurr and Toriel, and shared Kris's bedroom at Toriel's house before leaving for university. Asriel used to be in the local church choir, which sounded "thinner" after he went away. He was friends with Burgerpants, who nicknamed him "Azzy," along with Catty and Bratty, who both remember him fondly. Bratty convinced Asriel to give her his first kiss while playing truth or dare, and the Dreemurr family went to church almost every day for a week when Toriel found out. In the youth group, Asriel and Kris tried to make an angel doll like the one Noelle Holiday made for her father, but never finished because they spent the entire time on its giant wings.
Asriel also once tossed tasty cornflakes to Onion, who remembers him as friendly. One of the few people with something negative to say about Asriel is Catty's father, who refers to Asriel as "Doug" and "Douglas" and complains that Asriel didn't like his wife's cooking.
Asriel used to go to QC's Diner with his family on Sundays after service. After Toriel and Asgore separated, Asriel still took Kris there every Sunday to buy them hot chocolate, after which the two would sit in a corner booth and draw on the window with their breath. He also used to carry Kris to school when Kris woke up late.
Toriel mentions Asriel before Kris goes to school, excited that he is scheduled to visit home next week, and wonders if he will still enjoy "this little town" after university.
After Kris returns from the Dark World, several characters in Hometown can be spoken to about Asriel. Burgerpants has been saving up money to go to the same university as "Azzy." Asgore wonders if the family can go out to the diner together when Asriel visits, like old times. Berdly claims that Asriel has yet to return the book How to Draw Dragons, which is 2,583 days overdue and has accrued a massive fine.
While looking through the house the next day, Kris stumbles across How to Draw Dragons, and after noticing the purple character on the cover is dressed "immodestly," Kris concludes Asriel will never return the book. If Kris calls Toriel on their way to the library, Toriel assures them that if Berdly bugs them about Asriel's book she'll throw a smoke bomb so they can escape.
A door with a label that says "ASRIEL" appears at the Queen's Mansion. Upon interacting with the door, Kris closes their eyes while trying to peek through it, seeing nothing. If the party returns to the door after Susie and Ralsei rejoin, Susie peeks in the door and comments that Asriel is a massive nerd.
- Catty claims that the two had a romantic relationship, but it is implied that she may be exaggerating.
- Asriel might have been a part of the cross country club, since he owns a shirt with a rip in it.
- Toriel, when asked about Asriel at the end of Chapter 1, says that he likes the "green, egg laying lizard" from a game called "Super Smashing Fighters", which can be inferred to be a reference to Yoshi from the Super Mario Bros. series, and Super Smash Bros., a fighting game made by Nintendo. She also says that before she and Asgore separated, Asriel had a birthday party themed around it. Toriel also mentions that after Asgore cooked the eggs from the party, Asriel always hated a book about green eggs. This can be inferred as a reference to the children's book Green Eggs and Ham, by Dr. Seuss.
- When Father Alvin is asked about Asriel at the end of Chapter 2, he comments on how Asriel begged for forgiveness for dropping the same lizard into a pit. This is a reference to a practice in Super Mario World where Yoshi can be jumped off of once more mid-jump for additional height, sometimes dooming Yoshi to disappear off the bottom of the screen.
- Onion can be named "Asriel II."
- Religious ska CD under Asriel's bed is a contribution of Reid Young, a co-founder of Fangamer, by introducing Five Iron Frenzy to Toby Fox.
- In Chapter 2, if Kris inspects the computer in their room, there is a "poorly-drawn design for a game" that features a "last boss" with a "creature with giant rainbow wings". This references Undertale itself, the True Pacifist Route, and Asriel's counterpart's final form.
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