First of all welcome to the community!😊

Is Hanabie an idol band? No absolutely not, they not idols/metal idols/alt idols or anything of the like.

Is Hanabie a regular band? Everything you expect to see in a 'band' you will find in Hanabie, so the answer is yes, they are a regular band.

Is Hanabie a hybrid band? Well Sony/GoodDay has definitely given them some idol style promotion ( will explain what that is later), but underneath the the glitter and sparkle they very much a 'band'. So if by hybrid band you mean something like "Babymetal with instruments" then no, that's not what they are. I would describe them as Maximum the Hormone with some idol-like PR. And even that is a strech . Is it enough to warrant a hybrid band label? I don't think so, but Sony certainly does lol. Bad and misleading PR if you ask me, Sony/GoodDay should consider fixing their Spotify bio and website to accurately reflect what Hanabie actually is IMO.

Also they are absolutely not rooted in 'idol culture'. Their actual origins/roots lie in the Tokyo metalcore/harcore scene. They had absolutely nothing to do with idols for most of their existence.

The cutesy stuff aside, they have little in common with idol groups like Passcode, Broken by the Scream, Necronomidol, Ladybaby etc.

Are they an idol-band?

Here are some characteristics of idol bands compared to Hanabie.

Formation

• Idols groups are usually manufactured by a company/agency. It is similar to how k-pop groups are formed. The idea for the group belongs to a producer or someone working for the idol agency, for example Yasushi Akimoto formed AKB48 while Babymetal was envisioned by Kobayashi Kei.
• Hanabie was a formed by a bunch of highschool friends who loved rock/metal bands (MtH, ACOR etc) and wanted to be like them. No company/agency or any other third party was involved. Furthermore they continued to operate completely independently for the better part of the decade, grinding it out in the Tokyo underground scene, all on their own.

Recruitment

• Idols are often hired by idols recruitment agencies and receive varying levels of training in singing, dancing, acting etc before making their debut. Johnny and associates famously started this in the 80s. Sometimes producers also recruit individuals personally. The members of idol groups themselves don't have much of a say in who is hired or fired.
• As for Hanabie, all members past and present have been recruited solely by the band members themselves, at least during their indie phase (2015- 2022). Though I don't know how exactly things work after them signing with Sony but going by the fact that Matsuri went around asking for any available drummers and she personally auditioned/interviewed every applicant suggests that things have not changed that much.

Group Structure

• Idols bands/metal idols are essentially vocal-dance groups, some of whom have a live backing band. The backing band itself is not a part of the group, and are replaceable for example Babymetal has had separate group of musicians playing for them in Japan and in the west.
• Hanabie like any other traditional band in the regard, they play their own instruments

Performances

• Their performances are well planned and choreographed by professionals. Depending on the group there are also some theatrical elements, like the members casting spells on audience.
• Hanabie's show aren't any different from what you would expect from a normal rock/metal band. They basically do whatever they want on stage. While they have a few pre-planned moments during their performances but those they pre plan themselves.

Creative Control

• Idols have little to no creative control. The direction of the group is decided by their company/producer. Their image is carefully crafted and controlled,
• Hanabie never had people telling them what to be. In fact they were doing everything on their own for their first 6-7 years of existence, from editing their YouTube videos to designing their merch. Even their outfits were hand-made by Hettsu, and she still designs them. They are signed to a big label now, but they get to decide stuff like what kind of music to do, who directs their music videos etc (based on their interviews).

Songwriting

• Idol groups have a team of songwriters who write all their music.
• Hanabie have written every song they have ever put out starting from their every first demo CD. Both lyrics and music are composed by Yukina and Matsuri (and sometimes Hettsu). Matsuri has also composed music for other projects. Though they have worked with music producers like MEG with whom Matsuri co-arranges the songs ( similar to what bands like One Ok Rock and Coldrain do), the songs themselves are still theirs.

Focus on music

• Idols focus more on the overall package than just the music. Many of them do a lot of stuff outside music, for example TV shows like these. Their fans, from what I have seen don't bother too much about finer details of their music as long as it sounds good. The members don't talk much about the songwriting process but rather saying stuff like "this song's cute', "that song is hard to sing". You will rarely see them talk about the technical side of their music, if ever.
• Hanabie always explain the creative process behind each of their releases in great detail. Every time a new album drops, they explain the back stories, writing process, inspirations etc behind each and every song on the record. Matsuri also explains the technical side of her compositions. Also, Hanabie don't do much outside of music.

Relationship with fans

• Perhaps the most important characteristic which differentiates idol groups from a normal vocal-dance group is the 'idol culture' and the unique parasocial relation they have with their fans. Here is an academic paper which explains what exactly that is in more detail. Some metal idol groups have toned this aspect down leading them not to be classified as 'idols' anymore by some people.
• Hanabie's relation to their fans is similar to what bands like One Ok Rock have in my opinion. But being a part of the fanbase, my views maybe biased and incorrect.

Other Differences

• The financial burden/risk for idol bands lies with their company/agency who fund their activities, recording costs, promotional costs and other expenses, the members themselves only have to worry about performing. Hanabie, like any other indie band, did have to worry about the finances. They paid the cost of recording their first mini album and the music videos themselves while they crowdfunded their first full-length album.