Ok, I'm finally back.
New battlesuits have been released and the lore develops even further. I realize this series is somewhat niche so here's a TL;DR for those who don't want to read all the thread:
First there's the incorrect way of tagging including battlesuit names in the character tags, which is incorrect since the character is no different. There's also the fact that in a good number of occasions these battlesuits were not made especifically for these characters, I.e. they are massproduced or there more of them as shown in this panel of the manga.
e.g. Kiana Kaslana and Kiana Kaslana (White Comet), or Raiden Mei and Raiden Mei (Crimson Impulse)
Second is users using the character selection screen of the game as basis for character tags, which can lead to confusion since a lot of characters there do not have their actual name displayed for gameplay reasons. As result there are a good number of characters tagged incorrectly.
e.g. Theresa Apocalypse (Starlit Astrologos) who is not actually Theresa but Zhuge Kongming (Honkai Impact) who just looks like her, or Rita Rossweisse (Fallen Rosemary) who is not actually Rita but the Irene Adler of Honkai.
It's worth noting that miHoYo has made the separation between these characters clear several times, which can be seen in images or videos.
I would also like to point out that the previous point can also lead to people adding the tags of main characters to look-alike characters.
Converting Tags
The solution I propose for these issues is converting the battlesuit tags into general tags, except in some specific instances. That way it'll still be easy for people to find what the're searching while also cleaning the exesive amount of character tags and fixing the overlaping tags. It would also make cosplay tagging much more simple, just by adding the character_cosplay tag and the battlesuit general tag. Here's how I would do it:
Kiana Kaslana (White Comet) -> White Comet
Kiana Kaslana (Valkyrie Ranger) -> Valkyrie Ranger
Kiana Kaslana (Divine Prayer) -> Divine Prayer
Kiana Kaslana (Knight Moonbeam) -> Knight Moonbeam
Kiana Kaslana (Void Drifter) -> Void Drifter
Raiden Mei (Crimson Impulse) -> Crimson Impulse
Raiden Mei (Valkyrie Bladestrike) -> Valkyrie Bladestrike
Raiden Mei (Shadow Dash) -> Shadow Dash
Raiden Mei (Striker Fulminata) -> Striker Fulminata
Raiden Mei (Aeterba Purum) -> Aeterna Purum
Raiden Mei (Lightning Empress) -> Lightning Empress
Bronya Zaychik (Valkyrie Chariot) -> Valkyrie Chariot
Bronya Zaychik (Yamabuki Armor) -> Yamabuki Armor
Bronya Zaychik (Snowy Sniper) -> Snowy Sniper
Bronya Zaychik (Wolf's Dawn) -> Wolf's Dawn
Bronya Zaychik (Wolf's Dawn) -> Wolf's Dawn
Bronya Zaychik (Dimension Breaker) -> Dimension Breaker
Bronya Zaychik (Black Nucleus) -> Black Nucleus
Murata Himeko (Battle Storm) -> Battle Storm
Murata Himeko (Scarlet Fusion) -> Scarlet Fusion
Murata Himeko (Arctic Kriegsmesser) -> Arctic Kriegsmesser
Murata Himeko (Blood Rose) -> Blood Rose
Murata Himeko (Vermillion Knight) -> Vermillion Knight
Fu Hua (Valkyrie Accipter) -> Valkyrie Accipter
Fu Hua (Night Squire) -> Night Squire
Fu Hua (Phoenix) -> Phoenix
Fu Hua (Shadow Knight) -> Shadow Knight
Fu Hua (Azure Empyrea) -> Azure Empyrea
Theresa Apocalypse (Valkyrie Pledge) -> Valkyrie Pledge
Theresa Apocalypse (Sakura Rondo) -> Sakuno Rondo
Theresa Apocalypse (Violet Executer) -> Violet Executer
Theresa Apocalypse (Celestial Hymn) -> Celestial Hymn
Theresa Apocalypse (Twilight Paladin) -> Twilight Paladin
Yae Sakura (Gyakushinn Miko) -> Gyakushinn Miko
Yae Sakura (Flame Sakitama) -> Flame Sakitama
Kallen Kaslana (Sixth Serenade) -> Sixth Serenade
Rita Rossweisse (Umbral Rose) -> Umbral Rose
Rita Rossweisse (Phantom Iron) -> Phantom Iron
Rita Rossweisse (Artemis) -> Artemis
Rita Rossweisse (Vow of Roses) -> Vow of Roses
Rita Rossweisse (Icy Sea Spray) -> Icy Sea Spray
Rita Rossweisse (Hanafuda Oyabun) -> Hanafuda Oyabun
Seele Vollerei (Swallowtail Phantasm) -> Swallowtail Phantasm
Seele Vollerei (Stygian Nymph) -> Stygian Nymph
Bianka Durandal Ataegina (Bright Knight: Excelsis) -> Bright Knight: Excelsis
Durandal (Valkyrie Gloria) -> Valkyrie Gloria
Note: There are some battlesuits or costumes in the list that user specific in the story but still included due to easier tagging. Also some costumes are not tagged.
Particular Cases
Kiana Kaslana (Herrscher of the Void) I think we need a different approach because this is actually Sirin controlling Kiana's body. Leaving aside fan theories that arise from teases in the official lore, practically speaking and following Danbooru's rules Kiana and Sirin are two different characters. However, there's also the fact that Kiana is able to control that power by herself later in the story. We also need to take into account that even if there can be several instances of the same Herrscher, their clothing will always be different, so even if we have two different Herrschers of the Void their tags will need to be different. In Sirin's case she even has two different forms as Herrscher of the Void, normal and Ascendant. So this is what I would do:
Kiana Kaslana (Herrscher of the Void) -> Herrscher of the Void (Kiana Kaslana)
Sirin gets two new general tags:
Herrscher of the Void (Sirin)
Herrscher of the Void (Sirin) (Ascendant)
Now let's say I'm going to tag an image with Kiana Herrscher of the Void that's being controlled by Sirin:
Kiana Kaslana -> Her body.
Sirin -> The one in control.
Herrscher of the Void (Kiana Kaslana) -> The current Herrscher of the Void we are seeing.
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Raiden Mei (Herrscher of Thunder) is another interesting case since she has two Herrscher forms. First is this one which is the playable one, second is this one which is her first actual Herrscher form, appears in the manga and originates in Benghuai Xueyuan (Gun Girl Z). Here's what I suggest:
Raiden Mei (Herrscher of Thunder) -> Herrscher of Thunder (Raiden Mei) (Honkai Impact)
Herrscher of Thunder (Raiden Mei) (Benghuai Xueyuan)
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Bronya Zaychik (Herrscher of Reason) is a case quite different from the rest. There have been three Herrschers of Reason in the story of the Current Era, the first two, Welt Joyce and Welt Yang were male and Bronya is the third one. Curious thing with male Herrschers is that they do not get flashy costumes like female Herrschers, probably due to particular reasons in each case. Still, I think it'd be a good idea to add Bronya's name to the tag for consistency.
Bronya Zaychik (Herrscher of Reason) -> Herrscher of Reason (Bronya Zaychik)
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Herrscher of Sentience doesn't have tag yet, and she's also a new character. This is what I'd do:
Herrscher of Sentience (Hua). She already has the character tag Hua (Honkai Impact).
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Theresa Apocalypse (Starlit Astrologos) is Zhuge Kongming, a completely different character from Theresa but that looks like her. You can visit the wiki for more information.
Theresa Apocalypse (Starlit Astrologos) -> Starlit Astrologos This is Zhuge's battlesuit, she already has a character tag.
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Theresa Apocalypse (Luna Kindred) is a different character, just like Zhuge Kongming. In short, she originates in an event called Sanguine Nights and has a completely different backstory there. After that she has appeared in a variety of different events (not confirmed if it's the same Luna Kindred) and just like Zhuge she has a close connection with Captain. In the event she was also called Theresa, I believe her tag can be left as it is. Sometimes she's also called Tericula in a joking manner.
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Yae Sakura (Goushinnso Memento) is very weird. First she was introduced as a videogame character in a game made by Otto called Kallen Fantasy VII. After that Memento appeared in the main story as Sakura (without Yae) of the Previous Era, who was a comrade of Kevin Kaslana. I'd be fine with renaming the tag to Sakura (Goushinnso Memento) or Sakura (Previous Era) but I want to hear opinions first.
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Yae Sakura (Darkbolt Jonin) is Yae Kasumi who is a separate character. Practically speaking she's Yae Sakura from another universe and had a different backstory from a certain point. She originated in an event called Sanka Saga.
Yae Sakura (Darkbolt Jonin) -> Darkbolt Jonin This is her battlesuit tag, she already has a character tag.
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Kallen Kaslana (Ritual Imayoh) originated from the same videogame as Memento and has only appeared there. This basically means she is a different character of the actual Kallen. I'd personally rename the tag like this:
Kallen Kaslana (Ritual Imayoh) -> Kallen Kaslana (Kallen Fantasy VII) then add a general tag for the costume Ritual Imayoh
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Kallen Kaslana (Sin Hunter) is Kallen from the Sanguine Nights event, same event as Luna Kindred, meaning she's Kallen from an alternate timeline/universe. Not sure what to do with this one.
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Rita Rossweisse (Maid of Celestia) is Rita from Zhuge Kongming's universe. It can be left as it is but also need a general tag for the costume itself.
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Rita Rossweisse (Fallen Rosemary) is Irene Adler from an alternate timeline, she was introduced in an event called Rosemary's Floriograph. It was later revealed that she's actually a Rita that travels between bubble universes. She hangs in later events too with Zhuge in the Captain's Hyperion. Considering she was introduced as Irene Adler I think renaming the tag would be a good idea, especially since the reveal is supposed to be a spoiler. However, it's also worth noting that there's an actual Irene Adler and she even has art.
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Rozaliya Olenyeva (Fervent Tempo) is a different character from another universe, first introduced in Honkai Quest. She used to be Rozaliya but she changed after her accident and losing her sister. Now goes by the codename of Delta.
Rozaliya Olenyeva (Fervent Tempo) -> Delta (Honkai Impact)
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Seele Vollerie (Dream Seeker) is Seele from the same event as Delta.
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Durandal (Imperial Regalia) is Durandal from Zhuge's universe.
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Here's also like to rename the following tag:
Susannah (Honkai Impact) -> Susannah Manatt
There are other cases like Wendy where she is a Herrscher but not a playable character. I think it'd be a good idea to create a Herrscher tag for her too but I would also like to hear what people have to say.