Decent enough hurt/comfort Severitus. Nothing special, but nothing stupid either.
Plot summary
Beware: full spoilers! Also probably incomplete and possibly incomprehensible.
Neville dies on the first day of third years from injuries sustained at the hands of his uncle. The teachers react like humans: shocked, speechless (particularly Severus revisiting his behavious and preconceptions). Health checks are instituted. Harry downplays his injuries and tries to dodge the exam. Turns out things are pretty bad.
Snape reveals to Lupin that he is Harry’s father / sperm donor (without James’s knowledge because they had difficulty conceiving), with the help of a paternity hiding charm). He insists that he is not Harry’s father, but them being related makes a change of guardianship possible without Ministry involvement. He starts taking care of Harry a bit (new clothes, actually fitting glasses), under the assumption that the arrangement is temporary. Harry manages to misinterpret everything Snape says in the worst possible way.
Lots of hard fluff: turns out Harry has been unconsciously fixing his glasses for ages, for example, etc. At a meeting with Dumbledore, McGonagall and the Weasley parents, Severus discloses the whole affair, and the Weasleys agree to take Harry at the end of the year, if he wants to. Harry adopts Snuffles as his familiar.
Ginny tries to kill herself. Snape, with assistance of Pomfrey and McGonagall, saves her, which is really fucking hard apparently (spending some life energy), getting the shocked Harry to rethink who Snape is (who stated that he’d have done it on his own; which would have put him out of commission for at least a couple of months). Lots of anxiety and adults being good, Snape even figuring out that Hermione has ingested some of that potion during CPR, while utterly tired and nearly incapacitated. Flashback to him also attempting suicide as a teenager.
Severus needs a couple of weeks off after that and takes Harry with him, not content to leave him in a castle that Sirius Black has broken into. On the way, Snape arranges for Dudley to be placed with CPS and the Dursleys to think they have to flee from Death Eaters. Harry cooks and cleans for Snape, but doesn’t say anything, so that Snape assumes a house elf is taking care of him lol. He talks out loud to the “House Elf”, and Harry thinks he’s talking to him and all kinds of ridiculous miscommunication ensues. Harry again realises, after a tantrum, that Snape gave him his entire being when he said “This isn’t being nice, this is being responsible”.
Harry absolutely refuses to deal with Snuffle’s supposed death at the hands of Sirius Black and also tries to kill himself. Remus moves in with them to help with the suicide watch. We see Snape asa person most focused on responsibility and duty. Lupin has found Sirius in dog form and brings him, with a runic collar.
“Love can’t exist without Duty. Without responsibility, it’s nothing but a greeting card sentiment.”
The old neighbour invites them all for tea and suddenly magically remembers a box that Snape’s mom left with her before her suicide. After that, there are more drama cycles (Snape telling him about the prophecy etc) before the end, but you know how it goes. Oh also, Severus (due to the spell) and Harry (due to being his son) have appeared on the Weasly Clock.
Severus declines (in horror) the typical fulfillments of the life debt that would have Ginny be his betrothed or apprentice. He also finds out that he inherited the Prince fortune, which is seriously vast. Bill reveals that the spell Severus used allows people to speak to the dead (being necromantic in type), which means that his thoughts about what Lily would say may not be quite as theoretical as assumed.
Anyway, they need to resolve the life/soul debt, as it would be over Ginny’s head and prevent her from entering any other magical contracts, might automatically give all her wages to Severus, etc. The solution is a betrothal (with the expectation of dissolution once Harry turns 17) between Harry and Ginny, a very standard thing in the wizarding world. This works because Harry is “something Snape is willing to give his soul for”. But Harry doesn’t really want that, and he actually manages to say so. Instead, they resolve the matter by having Muriel Weasley fix the condemnation of Snape’s mother for her suicide.
Lily gets him to talk to Harry. Also tells him about Peter. Harry gets up his courage and tells Snape he wants to stay with him. Sirius is revealed to Dumbledore, who gets him off all legal hooks and wants to shove Harry off to him. The founders meet Minerva and Severus, our new baby necromancers, and pledge their support. However, Sirius has seen Severus and Harry and doesn’t want to come between them.