Well since Chiaki Naname have the role of some kind of Guardian Angel for the class 77 of hope's peak academy (or at least that's what I Understood) why don't use Digimon to make this role more literal and since Digimon Story Cyber Sleuth is the one with fits better and have the better conditions to proceed with this idea why not?

To beginning with this story I though about 3 main arcs the first one I would put 1 year after the events of Cyber Sleuth/Hacker's Memory and 3 years before Dangan Rompa 3: Zetsubō and main focus will be in build the relationship between Chiaki Nananmi and the cast of Cyber Sleuth plus Keisuke, their reunion with the Digimon and by consequence Chiaki meeting and becoming friend/partner With a Tailmon/Gatomon and will end by Chiaki convincing the Kamishiro Enterprises and the protagonists to let her volunteering in a project to link her mind to an online server (basically doing the same thing they did to Erika) to create a human mind backup prototype.

The second Arc will Start when Chiaki meet her fate at hope's peak academy but since her mind was already linked to the online server without anyone in the academy knowing all of Junko plans to spread Despair are leaked in enough time to the World at least create a Resistance against it at the same time the Chiaki's Mind server who developed enough to function as a second and independent mind for Chiaki is dealing with the pain the sorrow and the rage of what the death of her fiscal body will cause for her friends and to the world resulting in her with a huge help of the Tailmon deciding to find a way to save everyone from this tragedy resulting in a bio Marge Evolution to a Angewomon. After that is just the capture of remnants of despair that they can find using Chiaki's Memory Data and the involvement of the Kamishiro Enterprises and the cast of Cyber Sleuth in the New World program and with the Future Foundation.

And in the end, we have the goodbye despair with the addition of Chisa who was founded to be part of the ultimate despair earlier thanks to the leak of Junko's plans and instead of an AI Chiaki we have the Angewomon Chiaki who tanks to Arata and the Kamishiro Siblings help have some privileges to control the New World Program hidden in the Kernel of the Program. But for reasons (I have some but since this idea that I Know for sure that I can't write I will let the reasons open for the mind of anyone who decides to take this idea) can't use right from the Start, and a backup plans in case of hacking or someone's Avatar suffer enough damage to die.

About the digimon if we take this as Twin Aiba AU we will have about 33 slots for party digimon if we fallow the game's rule to be honest what digimon is there or not is the decision of the one who decided to give this Idea a Shoot (if they give) but i will put 2 recommendations

Beelzebumon: Blast Mode - this one is for fanservice and in both animes that this digimon have a big role (Tamers and Xros Wars) he is portrayed as someone who in some point of story starts to walk in a path of redemption despite being one of the seven demon lords digimon and did things that he himself agrees that are unforgivable he stop caring about it and decides that he only wants to do the right thing at least once. I think these ties with the class 77 and can create really good interactions.

Sakuyamon - this one is to fulfil the wise one role someone to give advices when the thing is not going very well or to guarantee a success

I think That's All the rest are details like Arata rejecting an invitation to study hope's peak academy as the Ultimate Hacker because a theat time he didn't feel like he deserves the title and other things like that.

so, bye bye. Please don't eat me alive because of my imagination.