The moment is serious. Some of Ironmouse’s tens of thousands of viewers are unhappy with the stream’s lack of structure. But Ironmouse maintains a wide-eyed, welcoming grin. It’s slightly unnerving — a byproduct of the fact that on Twitch she is not a flesh-and-blood person, but rather a pink-haired anime girl.

Ironmouse is the alter ego of a Puerto Rican Twitch star who’s kept her real identity anonymous and crafted an elaborate backstory in service of her online persona. Planning, she says, has never been her strong suit. In real life, she suffers from a chronic illness called common variable immune deficiency, or CVID, which leaves her highly susceptible to infection, as well as a lung condition. Even before the coronavirus pandemic, this has forced her to isolate from people and has, at various points, left her bedridden and on oxygen. She never knows when it might impact her, which makes it difficult to prepare for just about anything. And so, largely homebound, she disappears behind her digital avatar — known among Twitch and YouTube users as a virtual YouTuber, or “Vtuber” for short — and slips into the character of Ironmouse as an escape.

“I’m streaming because I want to hang out with people,” she says during her stream. “I want to have a good time and laugh. I want to make memories with people.”

Instead of broadcasting themselves on-screen using webcams, Vtubers use elaborate, often customized digital avatars as stand-ins. With the help of real-time motion capture software, these avatars mirror creators’ movements and lip sync along with what they’re saying, effectively functioning as digital marionettes. A Vtuber can look like just about anything, and the medium has allowed for an explosion of imagination. While the trend first gained notoriety in Japan in the early and mid-2010s, today, even some of the biggest Western live-streaming personalities have debuted their own Vtuber avatars.

Ironmouse’s marathon broadcast — during which she (and her avatar) even slept on stream, with friends and moderators entertaining viewers in her absence — ended on March 7, after 31 consecutive days. As far as numbers go, it was an unmitigated success. Viewers were able to extend the stream’s duration by subscribing with real money, and as days turned into weeks, Ironmouse broke the record for most-subscribed female streamer of all time and, eventually, most subscribers of any streamer on Twitch — though only at that specific moment (the record in that category is held by streaming celebrity Ludwig Ahgren, who accomplished the feat during a 31-day subscription marathon of his own in 2021).

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On Twitch, subscriptions cost viewers $4.99, with streamers pocketing 50 percent — and in some cases more depending on deals they’ve negotiated with the company. Ironmouse ended her marathon with nearly 172,000 subscriptions, meaning she took home hundreds of thousands of dollars. Following streamers on Twitch, meanwhile, is free, and Ironmouse broke records in that department as well: She’s now the most followed Vtuber on Twitch, surpassing all others in her rapidly growing field with over 1 million followers.

Ironmouse is far from an overnight (or over-month) streaming success. She began streaming back in 2017, after her dreams of becoming a professional opera singer — with training and schooling to show for it — were dashed by her condition.

“I originally started streaming because I was lonely and wanted something to do,” Ironmouse told The Post. “But I was very nervous and worried about being on camera because of my personal life.”

Inspired by a Japanese Vtuber named Kizuna AI, Ironmouse decided that she, too, would slip into the ageless skin of an anime character. But even then, she didn’t intend to create a backstory and persona for her character, or to become part of the Vtuber cinematic universe — then a gleam in the oversized cartoon eyes of a few personalities, now an industry full of collaborations and overlapping storylines that spans multiple countries, thousands of characters and even a handful of Vtuber-specific talent agencies.

“In my mind I was like, ‘Oh, I’m just a girl using an anime avatar on the Internet,’ ” she said. “But then as time went on, I started learning that there were other Vtubers, and I guess I’m a Vtuber too. I started developing the persona of Ironmouse, and she is me, but more like a coat. She’s a bigger version of me.”

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The climb to sustainable success was slow, with Ironmouse’s viewership numbers only really beginning to ascend toward Twitch’s upper echelon in 2020 and 2021. But it was nonetheless a gratifying journey. Ironmouse’s nascent fan base helped her craft an elaborate backstory for her character, who according to a fan-written wiki entry may be Satan.

“I think I just started saying, ‘Oh yeah, I’m Satan’ as a joke,” Ironmouse said. “Then more and more people started making the joke with me, and it just became my lore. … So yeah, I’m Satan, and that’s all there is to it.”

But even digital devils have dreams. Ironmouse knew for years she wanted to do a marathon stream, but when she first started, she could only sustain it for a couple hours at a time due to her health issues.

“I wanted to do a marathon stream so bad,” she said. “I was like, ‘If I ever get healthy enough, I’m gonna do it. I swear to God, I’m gonna do it.’ ”

Ironmouse lives in Puerto Rico, which receives less Medicaid funding from the U.S. federal government than states. As such, a marathon stream was out of the question until she began to blow up on Twitch, at which point she could finally afford higher-quality care.

“My health started improving because let’s be honest,” she said, “money helps with getting stuff.”

This allowed Ironmouse to push herself further — though initially, even the starting line of a marathon stream remained out of reach.

“I had a birthday stream that lasted seven hours,” she said. “I felt like I was gonna die after I finished that stream. I was like, ‘I can’t believe we did seven hours. Holy s---!’ ”

But she kept pushing. Last year, she hosted a charity stream that lasted 11 hours, at which point she began to feel like she might be ready to go for a day or more. While sickness ultimately delayed the marathon’s beginning, it finally kicked off in February this year. Ironmouse believed it would last two or three days, tops. Never in her wildest dreams did she imagine it’d go for a month. Viewers, well aware of her condition, expressed concern about how she was holding up. This led to a difficult dynamic: On one hand, she appreciated their concern. On the other, she disliked being treated like “a porcelain doll.”

“I’m so used to my family treating me like that, and I appreciate it because I know they love me, but I just really wanted people to treat me like a normal person,” she said. “I didn’t want anyone to think, ‘Oh, she’s just trying to get pity.’ I don’t want people to pity me or feel bad for me.”

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The marathon stream actually alleviated one of Ironmouse’s biggest illness-born issues: loneliness. Where other streamers like Ahgren have invited guests to their homes during marathons, Ironmouse’s condition left her physically isolated. Still, a rotating cast of streamer friends, chat moderators and viewers kept her company online despite living miles and oceans away.

“I had a lot of people ask me, ‘Isn’t it weird that you’re on stream all the time? Don’t you want your privacy?’ ” Ironmouse said. “But subathon was the only time I didn’t feel lonely because I felt like I had somebody there all the time. It was the least lonely I’ve ever felt in a long time.”

Ironmouse is hardly the only Vtuber to find success on Twitch, but many saw her all-out assault on the record books as evidence that Vtubers have finally made it. No longer a mere niche, they’re now part of Twitch’s mainstream. But increased attention also means additional scrutiny. Just a week after Ironmouse concluded her marathon stream, a controversial streamer named Quintin “Quin69” Crawford went on a rant about how Vtubers are “cheating” because they don’t need to do anything to look presentable, and how they “pretend to be 13 and put on some fake, cringe voice and create parasocial relationships with desperate [anime fans].” Not long after, Twitch users who shared similar views deluged Ironmouse’s chat with hateful messages — a practice known as a “hate raid” on Twitch.

Ironmouse, however, doesn’t think what she does is all that different from those who prefer the “flesh suit” status quo.

“At the end of the day, we’re all just streaming,” Ironmouse said. “There are people who don’t use a camera at all. There are people who use a PNG [image]. There are people who are Vtubers. … It’s just that I decided I want to look like a pink-haired demon from an anime show, you know?”

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Ironmouse also addressed comments about her voice, a singularly cutesy tool that she wields like (and sometimes as) an instrument. Contrary to popular belief, she said in her signature Ironmouse voice, which she maintained for the entire interview with The Post, it’s just her regular speaking voice. It’s another byproduct of her condition, which is known to cause repeated respiratory complications, she explained.

“I’ve had a fluctuating voice for a long time,” she said, attributing it to throat problems. “I’ve had issues in my personal life where people don’t take me seriously. They’re like, ‘Little girl, can I talk to your mom?’ I’ve had a couple streamers find my voice strange, but then I talked to them in private and they’re like, ‘Holy s---, it’s real!’ ”

Female streamers have complained for years about harassment on the platform and viewers making sexist comments in chat. Prominent male streamers have also accused women on numerous occasions of stealing their views, despite the fact that women are hard to come by in streaming’s upper echelons. Among the 200 most viewed streamers in February, only nine were women, according to data collected by the analytics firm Stream Hatchet. It’s noteworthy, then, that some viewers on Twitch find a fictionalized Vtuber image of a woman more palatable than many real ones — a phenomenon that echoes some of anime fandom’s more pernicious patterns. This raises thorny questions around Twitch’s culture, the future of Vtubing and sexism on the platform.

Still, Ironmouse insists she’s no different from any other female streamer — or streamer of any gender, for that matter. “Everybody is a real person, whether you use a flesh suit or not,” she said. “I just want people to know at the end of the day that we’re all just people on the Internet trying to have a good time. That’s all that matters.”

Contrary to what you might expect, Ironmouse says that getting to be somebody else on a regular basis has put her more in touch with herself than ever.

“I think with a lot of people who go through the motions of having a disease, sometimes you kind of forget who you are and lose yourself in the process,” she said. “I kind of became a zombie in my life. But with streaming, I feel like slowly I’ve been regaining pieces of me again and finding myself. I don’t feel like a zombie anymore. I feel more alive.”

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Ironmouse thinks the blowback she’s faced in recent times is symptomatic of larger growing pains. She expects that as Vtubers continue to gain ground on their fleshy counterparts, they’ll become more accepted.

“You can say the same thing about streaming years ago,” Ironmouse said. “All the adults were like, ‘Oh my God, it’s so strange. Why are you watching that?’ … And it’s OK if people don’t get it, because there’s always gonna be stuff some people just don’t get.”

Ironmouse said she sometimes dreams that she’s still in the midst of the marathon stream and wakes up feeling an urgent pull to resume streaming. But for now at least, it’s over. She’d like to do another someday, but to do so she’d have to get her moderators on board and push aside a number of behind-the-scenes obligations. In the meantime, she’s just trying to enjoy the moment. Despite a lifetime of health-born impediments, she’s living her dream — or a version of it, anyway.

“Because of my condition, [opera singing] was not meant to be,” Ironmouse said. “But it’s funny because I also always wanted to do something involving anime, which I thought was never gonna happen. And now all of a sudden, [both] are kind of happening right now, just in a different, twisted way. But I wouldn’t have it any other way.”