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Underground Defense Force -Sword and Sorcery and Swarm of Insects-

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Underground Defense Force -Sword and Sorcery and Swarm of Insects- screenshot 1
UDF PV trailerWatch trailer on Steam ↗

Underground Defense Force -Sword and Sorcery and Swarm of Insects-

Yakuentei · Published by Yakuentei · Official site ↗

Positive — 100% positive (19 reviews) · 25 achievements

Last updated 27 Sept 2026

Swarms of giant insects has appeared in the underground world "Agartha"! Defeat swarms of mutated insect monsters with multicast weapons/spells by your own party of customized characters! This is a casual turn-based tactical RPG with a focus on exhilaration and hack-and-slash system.

DJCTQ 10

£5.89

Lowest price we've ever recorded

View on Steam

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Price history

4 Sept 2026Lowest: £5.89 · Highest: £5.897 Oct 2026

Indie, RPG, Simulation, Strategy, Casual · 2024 · More £5 - £15 games

Explore the perilous underground world of Agartha as you lead your party through swarms of mutated insect monsters. Engage in thrilling, casual tactical battles using multicast weapons and spells in this indie RPG from Yakuentei.

About this game

About English language support


  • All UI texts, game system texts, and message window texts (including story) are translated in English.
  • But currently, flavor texts for missions, weapons, and armors are NOT translated.

"Love" the Mana! "Love" the Insects!


Mana (so-called MP) regeneration and "Emergency Charge" are important in this game. This is a casual turn-based tactical RPG (often called "SRPG" = simulation RPG in Japan) with a focus on exhilaration and hack-and-slash system.



Use weapons and magics that consume more than player characters' maximum Mana, bring them into the "Emergency Charge" state, recover Mana at ultra-high speed, and then blast the swarm of giant monsters (insects) on your next turn!

Then, get a lot of "XP", "Weapons", and "Armors" as rewards!



Some elements that are common in turn-based tactical RPGs are boldly omitted in pursuit of "Exhilaration" and "Fast Speed" so even inexperienced tactical RPG players and beginners can play without problems.

Of course, the game also has high difficulty settings such as HARDEST and INFERNO, which are intended for experienced players. (The "weapons" and "armors" obtained as rewards are also powerful)



Insects have grown to gigantic size because of the nuclear wars waged by our ancestors, the people on the "ground" of this earth.

Now that we can no longer live on the ground, let's fight as soldiers of UDF (Underground Defense Force) to protect the "underground world", the last sanctuary left to mankind!

UDF! UDF!!

"Love" the Mana! (Mana Regeneration & Emergency Charge)


In an ancient language that was called "Japanese" by a terrestrial civilization that became extinct in a nuclear war, the Kanji letter "愛" (= Love) was sometimes read as "Mana". Putting that aside...

  • "Mana Regeneration", the low-risk restoration

We UDF soldiers need "Mana" to swing our swords and cast magic. So we must "love" Mana.

When your Mana is running low, try to restore Mana by refraining from "Move" and "Action" as much as possible.

Depending on the armor you equip, you may be able to reduce the Mana regeneration penalty when "Move" or "Action".



  • "Emergency Charge", the high-risk restoration

In this game, you can use weapons and magics that consume more than player characters' maximum Mana.

Of course, your Mana will be depleted.

However, the "Emergency Charge" which occurs when your Mana becomes "negative" value, restores Mana very quickly, with or without "Move" or "Action".



The downside is that you are "unable to act" until your mana is "full"...

Conversely, there is "no disadvantage" if the excess amount (negative value) can be adjusted well so that the Mana will be full until the next turn!

If you can master it, you can cast a series of super-blast-range, super-high-power magic and eliminate swarm of insects in no time at all!

To achieve this, the combination of the Mana consumption of the "Weapons/Magics" you select on the equipment selection menu, and the Mana restoration performance of the "Armors" will be important.

"Love" the insects! (Summon Magic; "Mana Deshi" and "Mana Musume")


In this game, every few turns, a large number of insects emerge from their "Burrows".



"Some" subterranean people, who love insects very much, studied these burrows and invented summoning magic called "Mana Deshi" and "Mana Musume".

Translated notes:
  • "Mana" means "Love" in Japanese. (Also means "Magical Power")
  • "Mana Deshi" means "Beloved Disciple" in Japanese. (Also means "Magical Disciple")
  • "Mana Musume" means "Beloved Daughter" in Japanese. (Also means "Magical Daughter")

It means, by consuming "Mana", you can summon swarm of "cute" insects, like your "beloved" disciples or "beloved" daughters, as allied NPCs.



Especially in the higher difficulty levels, such as HARDEST and INFERNO, the risk of the defending character being knocked down increases.

It may sound pitiful, but sometimes it is necessary to use "Beloved Disciples" (Mana Deshi) and "Beloved Daughters" (Mana Musume) as decoys to avoid the biggest pinch.

"Love" yourself (= avatars)


The character customization system that is actively used in the works of "Yakuentei", the developer of this game, is also available.

In this game, players can customize their characters by selecting avatar parts.



Of course, all four party members can be changed their names.

As "Yakuentei" emphasizes "role-playing" for players, it is essential to implement a system that allows all party characters to be freely customized.

Story


In ancient ages, an advanced civilization flourished
on the ground of this planet, called "Earth"...

However, a final war called "nuclear war" broke out and they were destroyed...

Our ancestors, who could no longer live above the ground,
used the last remaining material resources to produce an artificial sun
and built this underground world, called "Agartha".

Although the advanced civilization was lost, our civilization
was able to develop and advance the magical technology with "Mana".
We have regained our happy days.

However, the creatures on the ground that survived the ancient nuclear war
have mutated under the influence of residual radiation.

Swarms of giant insects have invaded Agartha in order to eat us humans!

We have formed an allied force
to confront this threat, called "UDF".
(UDF = Underground Defense Force)

Now, you, the spearheads of the UDF, will face the
giant insects with the power of Sword and Sorcery!

UDF! UDF!!

Supports Steam Achievements and Cloud Save


"Steam Achievements" and "Cloud Save", which tend NOT to be supported by indie games developed by individuals, are both supported in this game.

The language (English or Japanese) will be also determined by reading the language settings of the Steam Client via the API.

This is NOT a game by a developer who cannot program, which is becoming increasingly common these days.

This game is developed by the author who can program and call the Steam API. You can rest assured.

About the distribution of videos, live action, etc.


Basically, you are welcome! No restrictions on video distribution such as preventing spoilers, etc.
(* But, please refrain from distributing videos that are intended to discredit the work.)

System Requirements

Will my PC run this? →

Minimum

Minimum:
  • Requires a 64-bit processor and operating system
  • OS: Windows 10, 11 (x64)
  • Processor: Intel Core Processor i5 or above, and 3rd Generation or above
  • Memory: 8 GB RAM
  • DirectX: Version 11
  • Storage: 300 MB available space

Recommended

Recommended:
  • Requires a 64-bit processor and operating system
  • Graphics: Display resolution 960x540 pixels or higher

Supported Languages

Japanese*
*languages with full audio support

Latest news

  • Patch NotesOfficial

    Update for Unity security vulnerability (v1.24)

    As already reported in the news, security vulnerability has been discovered in Unity game engine. Since this game also uses Unity, we have replaced the objects with clean-built ones using security-patched Unity (2022.3.62f2). Additionally, we performed the following maintenance to reduce file size and mitigate future security risks. Removal of unused Unity packages Update to latest version of Steam API (Steamworks.NET)
    Read full article on Community Announcements (SuzukiYE)
  • Community & EventsOfficial

    Participating in Steam Turn-Based RPG Fest 2024!

    This game "Underground Defense Force" (UDF) is participating in Turn-Based RPG Fest! We hope you'll take this opportunity to pick up if you are interested! https://store.steampowered.com/app/2603860 {STEAM_CLAN_IMAGE}/44677382/879716edca485e3f7f9e88a2b974dd8332ffe469.jpg
    Read full article on Community Announcements (SuzukiYE)
  • AnnouncementsOfficial

    English translation for story texts (v1.22 => v1.23)

    Following the previous update (see below), proceeded to translate the untranslated texts into English. https://store.steampowered.com/news/app/2603860/view/4599951478185432388 With this update, the story (in message window) and end roll are now available in English. The remaining is the summary text for weapons, armors, and missions. However, due to the volume of text, the number of characters limit of the UI, and the Japanese-unique content that is difficult to translate (*), we may not be able to proceed the translation soon. (*) For example, "Love" in Japanese language (= Kanji letter "愛") and "Mana" are read the same in Japanese, as they explained in this game. In English, "Love" and "Mana" are completely different each other, so simply translating them as they are does not make sense!! However, in addition to the fact that it would be beneficial to Yakuentei, the creator of this game, to support English, it is also true that this game "Underground Defense Force" is currently the most popular of all the games we have released so far, so we will continue to support English translations, taking into account the balance with the development of new games in the future, etc.
    Read full article on Community Announcements (SuzukiYE)
  • Patch NotesOfficial

    Some remaining English translation (v1.21 => v1.22)

    Some untranslated texts were translated into English. (Message windows in Mission 20, 27, 34, 37, 38.) On the next update, mission 39, 40, and end rolls will be translated. Overview texts for equipments (weapons/armors) and missions will be further later. Please note that due to the fact that this is an individual development indie game, I cannot guarantee that I will actually be able to proceed with the English translation, including determining the specific schedule. However, I will make my best efforts. Thank you for your understanding.
    Read full article on Community Announcements (SuzukiYE)
  • AnnouncementsOfficial

    Released a SLG bundle in collaboration with Flying Panjandrum!

    In collaboration with Flying Panjandrum, whose motto is to create "unserious but serious" games, we have released a SLG bundle! This unserious but serious title, "Underground Defense Force", is also included in this bundle, giving a 20% discount on the total of the three works. Even if you already own one or several of the titles, you can complete remaining titles for 20% OFF the total price of the unowned titles only, so those interested are encouraged to take advantage of this bundle! https://store.steampowered.com/bundle/43990 Note: Total amount displayed before adding to cart The total amount of this bundle displayed on Steam may NOT be subtracting the amount of items already purchased, but rather showing a higher amount that is the sum of all items. Once you add this bundle to your cart, they should be subtracted correctly. So, please confirm that the total amount is as intended before settlement.
    Read full article on Community Announcements (SuzukiYE)

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