This page discusses ending structure and contains spoilers. The full game contains multiple endings and branching routes, and the endings are decided by a combination of your interventions, your investigations and your final deductions - so there is no single checklist, but there are structural rules that explain how the routes work.
The store description is precise about the mechanism: "Your interventions, investigations, deductions, and choices will shape Tsumimi's stream and determine how the story ends." Four inputs, all of which you control, all of which feed the same outcome. Practically this means you are assembling a case file as you go, and the ending reflects what you managed to connect.
This is the single most useful structural fact in the game, and it catches out first-time players. Endings 6 and 7 only trigger after you finish the stream and sleep - the ending fires when you wake up, not when the last Mega Chat resolves. If you assume the stream's end is the run's end, you will think you have finished when you have not.
It also means your very last decision in a stream is not necessarily your last decision in the run - which is exactly why the developers tell you to save before entering a stream. The final beat happens outside the stream.
Documented examples of how a single Mega Chat opens a route:
Note what these examples show about the design: the price is part of the choice. A $1500 or $2000 Mega Chat is a large fraction of a limited budget, so committing to one route means not being able to afford another on the same night. The economy is the branching mechanism.
A single playthrough is roughly 3 to 4 hours, with the all-endings total listed at 4 to 5 hours on the original listing and later revised upward to around 8 to 9 hours for every ending. That gap is the real answer to how many runs you should expect - the difference between a short run and a complete one is roughly double, which is consistent with branching that rewards replaying the same days with different choices.
The game ships with official resources, which is unusual and worth using:
One practical warning about reception: the game's Steam reviews have been reported as "Mostly Negative" on at least one snapshot, at around 27% positive out of 161 reviews. The common thread in that reaction is that the game is short, the streams are long, and the endings arrive without the payoff some players expect. If you are deciding whether to buy, that is worth factoring in - and it is also an argument for using the demo first. The game also carries content warnings for psychological horror, violence and blood, and self-harm and suicide references, with jump scares used sparingly, and it is built around close environmental audio that is much better with headphones.