The 1st OVA focuses on Ilfa the maid robot aka HMX-17a designed by Sango Himeyuri, as she goes on what seems like a trial run at the Kousaka household.
By end of school things seem to be going normal (normal for the To Heart 2 universe that is, from Manaka being unable to keep the class attention, as in they leave just before she even starts making some announcement, to Yuuji making a quick getaway, to Sasara walking by carrying a pile of papers, to Sango and Ruri greeting Takaaki in their own ways, eg Sango going "Ruu" while Ruri red-eyes him, to Tamaki and Konomi getting him to go shopping with them, and he carrying the bags
). Later the latter trio reach Tamaki's house, and Takaaki makes an excuse to get out of there by faking a stomach ache.
Tamaki looks around and hears Yuuji talking, and walks in on him giving Ilfa a backrub. When Ilfa hears Tamaki talking to her, she gets up quickly giving Yuuji a headbutt to the chin and knocking him out (and she panics and checks on him), before formally introducing herself and explaining her presence here (this is followed by a flashback where Ilfa is at the Himeyuri's, talking with the twins and Takaaki, perhaps about the said trial, but Ilfa seems to have the idea that she was going to be at Takaaki's place and even fantasizes taking care of him, to the point that she imagines him saying "Aishiteru" to her, causing her to go all "moeeee", but she then gets dismayed when Takaaki mentions the Kousaka's place). Tamaki seems to agree to this after Ilfa and Yuuji explain things (Yuuji being frantic about it).
Overall Ilfa's doing well as a maid (cleaning the house, cooking, and doing the laundry - very good in fact, in my opinion surpassing her predecessors Multi and Serio overall), if only Yuuji doesn't keep spying on her in indecent ways with a video cam (eg focusing on her underside when she's cleaning the front porch by crawling, looking up her skirt when she's cooking, and peeking at her when she's bathing), at least Tamaki knocks some sense into him (in the process destroying whatever video camera he used - and they get older they're destroyed, from a mini-DVD camcorder to a hi-8 model to VHS
), but Ilfa seems ignorant about it. Then Tamaki starts teaching Ilfa a thing or to about, um, "responsibility", like criticizing Yuuji for poor table manners, then bugging him about his homework (and tutoring him like a strict teacher), then yanking his blanket off when he refuses to wake up for school (i.e. she's doing things that Tamaki herself would normally do to Yuuji).
The night of Ilfa's last day, she has a talk with Tamaki and whispers something to her, and Tamaki agrees to it. Next morning Ilfa is leaving (with Yuuji crying that she is). Just before she leaves, she says something that apparently pleases Yuuji, before she suddenly grabs him in the face Tamaki-style and holds him in the air for a few moments before Tamaki gives the nod to drop him.
The credits show a few interesting scenes, including Konomi trying on HMX-12 robot ears!
After the credits there's an omake featuring Manaka, Yuma, and Karin at a restaurant trying to decide what to eat. Yuma seems to be stalling everyone for some reason (i.e. preventing Manaka and Karin from hitting the portable chime on the table that would summon a waitress to get their order). Seems Yuma wants to get the best meal, but as she contemplates on an item, Manaka and Karin end up choosing that item each time, making Yuma really upset. Later Yuuki (yep the girl who shows up at night in the game) comes out of the ladies room and joins the trio sitting next to Karin (apparently she's good friends with Karin here), then upsets Yuma again with her menu choice. Karin then gets ready to hit the waitress chime, but Yuma swats Karin's hand away, in the process flinging the chime into the air, before it hits Yuma on the forehead and lands on its button, sounding off. Yuma gets really pissed and decides to walk out, before turning on everyone with her "You won't beat me!" catchphrase, but she's interrupted by the waitress, who turns out to be Marianne.