In Milfeulle's route, Tact shows he's willing to put up with all sorts of random crap just to make Milfeulle feel like she's not completely bad luck.
In Ranpha's route, managing to do the impossible and buy Ranpha a pair of shoes that aren't for sale, and then doing the impossible again by managing to salvage Ranpha's evening despite the shoes she herself demanded being too big and Ranpha feeling like she personally ruined everything.
In Mint's route, by the skin of his wits and by his love for Mint, he manages to rescue Mint from being imprisoned in her own home by her father, and repair a father-daughter relationship that had been estranged for years, in one single BigDamnHeroes scene.
The manner in which he deals with Vanilla's agony and grief after her beloved pet rabbit, Ugiugi in the Japanese version and Bunbun in Aroduc's translation, dies is near saintlike; he says all the right things, manages to deal with all of Vanilla's underlying demons in the space of a few minutes, and is completely respectful to what is essentially the death of a pet. Vanilla's reaction to his handling of the situation is to ask him if they could stay "like this" (holding each other) a while longer. That's right, by virtue of his sheer niceness, Tact managed to get a 13-year-old girl from sobbing her eyes out over the death of a pet to shyly asking to prolong a hug. Even if this weren't a romantic route per se, and it is, the scene would still be heartwarming even if Vanilla was just Tact's sister or daughter or something.
Galaxy Angel Moonlit Lovers, second videogame
In Ranpha's route, Tact intentionally makes a complete ass of himself by dressing up in a Ranpha-fanboy-outfit and doing an extremely corny love cheer, just to prove to Ranpha that he's perfectly willing to keep up with Ranpha's fast pace and romantic over-enthusiasm if that's what it takes to love her.
In Chitose's route, Tact clears up Chitose's trauma over her deceased father in a single scene so she won't pointlessly sacrifice herself against Nefuria in the GA-007 and so Chitose will allow Tact to be with her.
Galaxy Angel Eternal Lovers, third videogame
In Ranpha's route, risking his life to save Ranpha from a burning building by catching her as she jumps, which permanently erases Ranpha's previous traumatic reflex of striking Tact whenever he touched her.
In Mint's route, Screaming "I LOVE MINT!!!!!!!!!" into the Elsior's loudspeaker at the top of his lungs so everyone in the entire ship can hear him, and then launching into a loud speech about how much he loves Mint, how much he wants to hold her close, and kiss her all day long, and all of that just to wake Mint from an "exhaustion coma" caused by her romantic turmoil. It works, although Mint at first gets pissed off at Tact for saying embarrassing things like that for the whole ship to hear, but Tact was clearly willing to pay the price of Mint being mad at Tact for a few minutes to make sure Mint's all right.
Later in the same route, managing to find Mint buried in rubble and rescuing her after they had an argument over Mint's emotional shyness and sudden distance, by managing to hear Mint's voice when no one else could. Another BigDamnHeroes example, just like in Mint's route from the first game.
In Vanilla's route, he teaches himself to knit to prove his love for Vanilla. Then he tops himself by proposing marriage in a manner that clears up all Vanilla's romantic fears at once and causing her malfunctioning nanomachine pet to return to normal. Then he tops himself a third time (although this one's not stated directly, the player has to make an inference) because when he gives Vanilla an engagement ring, her name is engraved on it. That means Tact can't take this ring back to the store because it technically counts as "damaged," his commitment is permanent, despite Vanilla's still-too-young-age. Clearly Tact is willing to wait.
In Chitose's route, after a lot of false attempts, Tact and Lester finally manage to figure out a way to break Chitose of her delusion that she loves Lester. It turns out they had to do it in stages (Tact and the Angels were trying all-at-once zany schemes before like writing love letters and romantic re-enactments); first Lester has to explain to Chitose that he's not her boyfriend, and then Tact has to finally bite the bullet and do something he's been avoiding out of sheer nerves: tell Chitose flat-out, to her face, that he loves her and wants her to go out with him. That doesn't really seem very heartwarming, but it does reflect Tact's usual tendency to be willing to put himself out on a limb for the woman he loves.
The "kiss scene" in the simulated park at night against the stars in Milfeulle's, Vanilla's, and Chitose's routes. It's the "first kiss" for Vanilla or Chitose, and in Milfeulle's case it's not their first kiss because Milfeulle already had her "second first kiss" earlier in the game back when she still had amnesia. There's no "kiss scene" in that spot with Ranpha, Mint, or Forte, but their scenes are just as heartwarming: Ranpha doesn't get a CG but the conversation is romantic, Mint allows Tact to lay his head in her lap, and Forte and Tact converse about their future over drinks. This moment, whether kiss or conversation or laying down or drinks, is even more heartwarming considering that in Eternal Lovers, Tact had to go through hell just to prevent his relationship with chosen Angel from ending for good. That's why this game is called Eternal Lovers.
The moment when Tact finally proposes marriage! In Vanilla's route, it makes Vanilla so surprised-but-happy that her malfunctioning nanomachine pet returns to normal. In Milfeulle's route, it happens near the end, and it actually takes Milfeulle a few seconds to register what Tact just said. Then Milfeulle blushes like crazy and stammers a lot, but she joyfully accepts. Ranpha gets an indirect marriage proposal; Tact wants to meet Ranpha's siblings since they'll be his future in-laws. It takes a second for Ranpha to get it, but the only way her siblings could be Tact's future in-laws is if Ranpha married Tact. There's no formal marriage proposal in Mint's, Forte's, or Chitose's routes (Mint and Forte just kind of take it for granted that they'll be together forever with Tact and that that implies marriage, although Mint is much more affectionate about it than Forte, and Chitose's romantic relationship started really late since they didn't even officially "get together" until the third game, so Tact and Chitose end up starting to date instead, but they still end up married by Galaxy Angel II).
Galaxy Angel II Zettai Ryōiki no Tobira, first Galaxy Angel II videogame
When Tact reunites with whoever was chosen as his wife after respective duties kept them from seeing each other for a bit. Each Angel gets her own romantic CG depending on which Angel is Tact's wife. Milfeulle and Tact hold hands, Ranpha affectionately touches Tact's lip while the both of them scream at the top of their lungs how much they love each other ("Darling!" "My honey!"), Mint goes for a combination "hug/holding hands" and she lays her head on Tact's chest, Forte hugs Tact, Vanilla rushes into Tact's outstretched arms while looking up at him and smiling, and Chitose hugs Tact and lays her head on Tact's shoulder/neck. This is kind of a meta-example, though: it is extremely rare for a romantic couple in a franchise to cover the gradual development of the romantic relationship, and then cover their married life in the future, and then portray this married life positively, like Tact and the Angel's love for each other has not faded with marriage.