Information about ハイパートンネルズ&トロールズ “Hyper Tunnels & Trolls” (1991) in the English speaking world is scant, but think I can answer some of the questions I’ve seen people ask!
Miyuki Kiyomatsu, who did the game design for Sword World, contributed a T&T column to Warlock magazine. From Dec. ’89 to Aug. ’90 his column was called “How to Make Hyper Tunnels & Trolls”. Much of the content that would eventually appear in the 448 page bunkobon by Shakaishisosha first appeared there. Development and test play took place at Group SNE.
The 1991 version is a complete set of rules recapitulating the content from 5th edition T&T needed for play. The races are the same: human, elf, dwarf, hobbit, fairy, and leprechaun, as are the ability scores: strength, intelligence, luck, constitution, dexterity, and charisma. Kiyomatsu admired the T&T combat system, calling it fast paced and exciting, so he left it as is. To the 4 classes: 戦士 “warrior”, 盗賊 “rogue”, 魔術師 “wizard”, and 魔法戦士 “warrior-wizard”, HT&T adds 6 more: 武闘家 “martial artist”, 僧侶 “priest, 聖闘家 “holy warrior”, 怪盗 “phantom thief”, 呪術師 “shaman”, and 魔道士 “sorcerer”. New spells are a significant portion of the new content.
When Group SNE published a Record of Lodoss replay in Warlock magazine using the T&T rules, they dropped Etoh the cleric. If they had the HT&T rules they could have made Etoh a priest, which approximates the cleric of Dungeons & Dragons. Like wizards, priests must expend strength to cast spells. Some spells require the priest to have a minimum charisma. There are priest spells for detecting, turning, and destroying undead.
HT&T adds a skill system. Every skill is associated with an ability score. If the character has a skill he has a skill level for it from 1 to 9, though just how high the level can go depends on the skill. Saving throws in T&T are ability score checks: the player rolls 2d6 and adds the relevant ability score. Skill checks add the character’s skill level to the roll too. HT&T awards characters a number of “hyper points” equal to their level at the start of each adventure. These can be spent to increase the number of dice used in saving throws and skill checks. Each point spent adds one die.